Elements and Compounds - Definition, Example, Types, Classification, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:32 PM IST

Classification of Matter:

Chemistry is the study of different types and properties of matter. We see different types of components and materials all around us. It is therefore essential to classify and categorize them so that they can study, analyze and understand their characteristics easily of elements compounds, and mixtures. The matter around us can be classified as pure matter and impure matter. Those with fixed chemical composition are pure substances. A pure substance is divided into elements and compounds. Since impure substances are substances that may have different compositions and therefore do not have any fixed characteristics thus, they can't be divided into elements and compounds.

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Classification of Matter:
What is an Element?
Examples of Elements:
Types of Elements:
What is a Compound?
Examples of Compounds:
Types of compounds:

Element Compounds

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What is an Element?

A substance that cannot be broken down into simpler components using chemical methods or A substance composed of atoms with one atomic number is called an Element. An element meaning is a complete chemical substance that constitutes an entry in the modern periodic table. Elements and compounds are made up of only one type of atom and two or more elements and compounds respectively. They cannot be broken down into simpler fragments and can exist in the form of atoms or molecules. The elements are represented by symbols, issued by IUPAC. For example, Hydrogen is represented by H, Nitrogen is represented by N, and so on.

Examples of Elements:

Below we have listed 10 examples of elements,

Element	Symbol
Hydrogen	H
Helium	He
Lithium	Li
Beryllium	Be
Boron	B
Carbon	C
Nitrogen	N
Oxygen	O
Fluorine	F
Neon	Ne

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Types of Elements:

Elements are classified into metals, non-metals, and semi-metals according to their properties.

Metals Non-metals Metalloids

Metals: Metals are the electro positivity elements that tend to lose electrons in order to achieve stability. Metals have physical characteristics such as hardness, high stresses, lusters, conductivity, high melting and boiling points, etc.

Examples: Iron (Fe), Sodium (Na), Calcium (Ca), Lead (Pb), etc.

Non-metals: Non-metals are the elements that tend to get electrons, i.e. they are electron-negative. They are not metals. Non-metallic physical properties include fragility, comparatively less strength of the tensile materials, brightness, non-conductivity or isolation, lower melting and boiling points, etc.

Example: Hydrogen (H), Chlorine (Cl), Iodine (I), Phosphorus (P), etc.

Metalloids: Metalloids are elements with properties between metals and nonmetals.

Example: Boron (B), Germanium (Ge), Silicon (Si), etc.

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What is a Compound?

We know that compound definition is a pure substance. Also, the compound definition in chemistry is when two or more elements are chemically combined in a fixed weight ratio, the resulting product is a compound. A compound can be defined as a substance composed of two or more different types of elements in a fixed atomic ratio or A compound is made up of two or more atoms of different elements that are connected to each other. Some individual attributes of the element are lost, and the newly formed connection acquires new attributes. Now questions arise: what is a compound in Chemistry? It is a compound represented by its chemical formula. The chemical formula is a symbolic representation of the atomic ratio constituting a specific compound. For example, water H₂O is a compound. Here we can see that Water is made up of two hydrogen atoms and one oxygen atom ( Look into the below image).

H2O (Water)

Examples of Compounds:

Below we have listed 10 examples of compounds,

Compound	Formula
Water	H₂O
Sulphuric Acid	H₂SO₄
Alcohol	C₂H4_O
Common Salt	NaCl
Nitrous oxide	N₂O
Carbon Dioxide	CO₂
Glucose	C₆H₁₂O₆
Ammonia	NH₃
Acetic Acid	C₂H₄O₂
Copper sulphate	CuSO₄

Someone may ask, How many compounds are there? More than 350,000 compounds (including chemical mixtures) are registered for production and use worldwide. Also what is an element in chemistry it is a compound that can be transformed into another chemical substance by a chemical reaction with a second substance.

NCERT Chemistry Notes :

Types of compounds:

Compounds can be categorized as ionic and covalent compounds on the basis of formation.

Ionic compound and Covalent Compounds

Ionic Compound: Between metal and non-metal, ionic compounds are formed. They are also known as electrovalent ion compounds. The metal atom is cation-forming and the non-metal atom is forming an anion. Electrons are anions.

Examples: sodium chloride, calcium oxide, etc.

Covalent compound: Between two non-metals covalent compounds are formed. It is also known as a molecular compound. The electrons are formed by the sharing of two or more nonmetals.

Example: water, carbon dioxide, methane, sugar, etc.

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Frequently Asked Questions (FAQs)

1. 1. What is a mixture? Give an example.

Mixtures are structures that are physically combined and can be separated into original components. One type of atom or molecule is a chemical substance for elements and compounds. A combination is made up of various kinds of atoms or molecules not chemically linked.
Example: A mixture of Sand and water, salt and water, etc.

2. 2. What are the properties of compounds?

Compound meaning is that which always contains the same element definition in chemistry in the same proportions; for example, each carbon atom in carbon dioxide always has two oxygen atoms, and each oxygen atom in water always has two hydrogen atoms. The entire structure of a compound is always identical.

3. 3. What is the difference between Mixture, elements and compound ?

Element definition is a substance that is made up of only one atom form. A compound is a material consisting of more than one bonded atom. A mixture is a combination of two or more unbounded compounds or compounds, each of which retains its own properties.

4. 4. Is water is an element or compound? Why?

Water is a compound because it contains more than one element that is hydrogen and oxygen combined in the ratio of 2:1.

5. 5. Is gold Element, Compound, or Mixture?

Gold is an Element. Gold is Element 79 in the periodic table and the symbol of gold is Au. In fact, there are 118 elements and compounds in a periodic table.

6. 6. Mention any four Compounds and their uses?

Water: For drinking and as a solvent.
Table salt: A key part of our daily diet, meat, and fish preservatives.
Sugar: Used as a Sweetener, flavoring, and as a coloring agent.
Methane: Used as natural gas and as a fuel.

7. 7. Which of the following is a compound

air
water
oxygen
iron

Ans. Option (b) is correct.

8. How do covalent compounds differ from ionic compounds in terms of their properties?

Covalent compounds are formed by sharing electrons between non-metal atoms, while ionic compounds are formed by the transfer of electrons between metals and non-metals. Covalent compounds typically have lower melting and boiling points, are often gases or liquids at room temperature, and do not conduct electricity in solution. Ionic compounds are usually solid at room temperature, have higher melting and boiling points, and conduct electricity when dissolved in water or molten.

9. What is the relationship between a compound's structure and its properties?

A compound's structure, including its molecular geometry, bond types, and intermolecular forces, directly influences its properties. For example, the tetrahedral structure of methane (CH4) results in a non-polar molecule, affecting its solubility and boiling point. The hydrogen bonding in water (H2O) explains its unusually high boiling point for its molecular weight.

10. How do isomers differ, and why are they important in chemistry?

Isomers are compounds with the same molecular formula but different structural arrangements. They can have significantly different physical and chemical properties despite having the same atoms. For example, butane and isobutane are isomers with the formula C4H10, but they have different boiling points and reactivity. Understanding isomers is crucial in organic chemistry and biochemistry.

11. How do amphoteric compounds behave differently from acids or bases?

Amphoteric compounds can act as both acids and bases, depending on the reaction conditions. They can donate protons in some reactions (acting as an acid) and accept protons in others (acting as a base). For example, aluminum hydroxide Al(OH)3 can react with both acids and bases. This dual nature is important in understanding buffer solutions and certain biochemical processes.

12. Why do some compounds form crystals while others don't?

Crystal formation depends on the intermolecular forces and the ability of molecules or ions to pack in a regular, repeating pattern. Compounds with strong, directional intermolecular forces (like ionic compounds or those with hydrogen bonding) are more likely to form crystals. The size and shape of the molecules or ions also play a role. For example, sodium chloride (NaCl) easily forms cubic crystals due to its ionic nature and simple structure.

13. What is the relationship between atomic mass and molecular mass?

Atomic mass is the mass of a single atom of an element, while molecular mass is the sum of the atomic masses of all atoms in a molecule. For compounds, the molecular mass can be calculated by adding up the atomic masses of each element multiplied by the number of atoms of that element in the molecule.

14. How does the octet rule explain the formation of chemical bonds?

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons (like noble gases). This drives the formation of chemical bonds. For example, sodium loses one electron and chlorine gains one electron to form an ionic bond in NaCl, both achieving stable octets.

15. How does the concept of electronegativity influence the type of bond formed between elements?

Electronegativity is the ability of an atom to attract electrons in a chemical bond. When there's a large difference in electronegativity between two elements, they tend to form ionic bonds (electron transfer). When the difference is small or zero, they form covalent bonds (electron sharing). The greater the electronegativity difference, the more polar the covalent bond becomes.

16. Why do some compounds sublime instead of melting?

Sublimation occurs when a solid transitions directly to a gas without passing through the liquid phase. This happens when the vapor pressure of the solid is greater than the atmospheric pressure at temperatures below its melting point. Compounds with strong intermolecular forces in the solid state but weak forces in the liquid state, like dry ice (solid CO2), are prone to sublimation.

17. How does the concept of oxidation state help in understanding compound formation?

Oxidation state (or oxidation number) represents the degree of oxidation of an atom in a compound. It helps in tracking electron transfer in reactions, balancing redox equations, and predicting the formation of compounds. For example, in H2O, hydrogen has an oxidation state of +1 and oxygen -2, indicating that oxygen has gained electrons from hydrogen in forming the compound.

18. How do isotopes affect the properties of compounds?

While isotopes of an element have the same chemical properties, they can affect a compound's physical properties due to mass differences. For example, heavy water (D2O, where D is deuterium) has a higher boiling point than regular water (H2O). Isotopes can also affect reaction rates (kinetic isotope effect) and are important in radioactive dating and nuclear chemistry.

19. How does the concept of hybridization explain the formation of multiple bonds?

Hybridization explains how atoms can form multiple bonds by mixing atomic orbitals to create new hybrid orbitals. For example, in ethene (C2H4), each carbon atom undergoes sp2 hybridization, leaving one unhybridized p orbital. These p orbitals overlap to form a pi bond, resulting in a carbon-carbon double bond. This concept is crucial for understanding the structure and reactivity of many organic compounds.

20. Why are some elements more reactive than others?

The reactivity of elements is primarily determined by their electron configuration and position in the periodic table. Elements with incomplete outer shells tend to be more reactive as they seek to achieve a stable electron configuration by gaining, losing, or sharing electrons.

21. How do isotopes of an element differ from each other?

Isotopes of an element have the same number of protons (atomic number) but different numbers of neutrons. This results in atoms with the same chemical properties but different atomic masses. For example, carbon-12, carbon-13, and carbon-14 are all isotopes of carbon with 6, 7, and 8 neutrons, respectively.

22. Why do some elements exist as diatomic molecules in their natural state?

Some elements, particularly non-metals like hydrogen (H2), nitrogen (N2), and oxygen (O2), exist as diatomic molecules because this configuration is more stable than individual atoms. The shared electrons in these molecules create a lower energy state, making the diatomic form more favorable.

23. How does the periodic table help predict the types of compounds elements will form?

The periodic table organizes elements based on their electronic structure, which determines their chemical behavior. Elements in the same group tend to form similar types of compounds. For example, alkali metals (Group 1) typically form ionic compounds with halogens (Group 17). The position of an element in the table can predict its valence, oxidation states, and the types of bonds it's likely to form.

24. What is the significance of bond order in determining a compound's stability?

Bond order represents the number of electron pairs shared between two atoms in a molecule. Higher bond orders generally indicate stronger and shorter bonds, which often result in more stable compounds. For example, the triple bond in nitrogen (N≡N) contributes to its stability and relative inertness compared to other diatomic molecules.

25. How do allotropes of an element differ from compounds?

Allotropes are different structural forms of the same element, while compounds are made up of different elements. For example, diamond and graphite are allotropes of carbon, both containing only carbon atoms but with different structures. In contrast, carbon dioxide (CO2) is a compound containing carbon and oxygen.

26. Why do some compounds conduct electricity when dissolved in water while others don't?

Compounds that conduct electricity when dissolved in water are called electrolytes. They dissociate into ions in solution, allowing for the flow of electric current. Non-electrolytes do not form ions in solution and therefore do not conduct electricity. For example, sodium chloride (NaCl) is an electrolyte, while sugar (C12H22O11) is a non-electrolyte.

27. How does the law of constant composition apply to compounds?

The law of constant composition states that a pure compound always contains the same elements in the same proportion by mass, regardless of its source or method of preparation. For example, water (H2O) always contains hydrogen and oxygen in a 1:8 mass ratio, regardless of whether it comes from a tap, ocean, or is synthesized in a lab.

28. What is the difference between a molecular formula and an empirical formula?

A molecular formula shows the actual number of atoms of each element in one molecule of a compound, while an empirical formula shows the simplest whole-number ratio of atoms of each element in a compound. For example, the molecular formula of glucose is C6H12O6, while its empirical formula is CH2O.

29. Can compounds be separated into their constituent elements using physical methods?

No, compounds cannot be separated into their constituent elements using physical methods. Chemical methods are required to break the chemical bonds between the elements in a compound. Physical methods can only separate mixtures, not compounds.

30. What is the difference between an element and a compound?

An element is a pure substance made up of only one type of atom, while a compound is a substance made up of two or more different elements chemically bonded together in a fixed ratio. For example, oxygen (O2) is an element, while water (H2O) is a compound.

31. What is the significance of valence electrons in chemical bonding?

Valence electrons are the outermost electrons of an atom and are involved in chemical bonding. They determine an element's chemical properties and how it will interact with other elements. Elements with similar valence electron configurations often have similar chemical properties, which is reflected in their grouping in the periodic table.

32. What is the difference between empirical and molecular formulas, and why are both important?

An empirical formula represents the simplest whole-number ratio of atoms in a compound, while a molecular formula shows the actual number of atoms in one molecule. Both are important because the empirical formula is useful in determining the composition of unknown compounds through experimental data, while the molecular formula provides the exact molecular structure. For example, the empirical formula of glucose is CH2O, while its molecular formula is C6H12O6.

33. How do intermolecular forces differ from intramolecular forces?

Intramolecular forces are the strong chemical bonds within a molecule (like covalent or ionic bonds), while intermolecular forces are the weaker attractions between molecules (like hydrogen bonds or van der Waals forces). Intramolecular forces determine a compound's composition, while intermolecular forces influence its physical properties like boiling point and solubility.

34. Why do some compounds have a dipole moment while others don't?

A dipole moment occurs in molecules where there is an uneven distribution of charge due to differences in electronegativity between atoms. Polar molecules have a net dipole moment, while non-polar molecules don't. The overall shape of the molecule also plays a role; for example, CO2 is non-polar despite having polar bonds because its linear structure results in the dipoles canceling out.

35. What is the significance of the atomic number in identifying an element?

The atomic number is the number of protons in an atom's nucleus and uniquely identifies an element. It determines the element's chemical properties and its position in the periodic table. Atoms with the same atomic number are the same element, regardless of the number of neutrons or electrons.

36. How does the concept of electronegativity explain the polarity of bonds and molecules?

Electronegativity is the ability of an atom to attract electrons in a chemical bond. When two atoms with different electronegativities bond, the electrons are not shared equally, resulting in a polar bond. The overall polarity of a molecule depends on both the polarity of its bonds and its geometry. For example, water (H2O) is polar because oxygen is more electronegative than hydrogen, and the molecule has a bent shape that doesn't allow the bond dipoles to cancel out.

37. How does the concept of resonance explain the stability of certain compounds?

Resonance occurs when a molecule or ion can be represented by multiple valid Lewis structures. The actual structure is a hybrid of these resonance forms, which often results in greater stability than any single structure would suggest. For example, the benzene molecule's stability is explained by resonance between two equivalent structures, resulting in a more stable aromatic ring.

38. Why do some compounds decompose when heated while others don't?

Thermal decomposition depends on the strength of chemical bonds within a compound and the stability of the potential products. Compounds with weaker bonds or those that can form more stable products (like gases) are more likely to decompose when heated. For example, calcium carbonate (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide (CO2) when heated, as the products are more stable at high temperatures.

39. How does the concept of hybridization explain the geometry of molecules?

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which can explain molecular shapes that don't fit the basic VSEPR theory. For example, the tetrahedral shape of methane (CH4) is explained by sp3 hybridization of carbon's orbitals. This concept is crucial for understanding the three-dimensional structure and reactivity of many organic compounds.

40. What is the relationship between a compound's formula mass and its molar mass?

Formula mass is the sum of the atomic masses of all atoms in the formula unit of an ionic compound or in one molecule of a molecular compound. Molar mass is the mass of one mole of the compound, which is numerically equal to the formula mass but expressed in grams per mole (g/mol). For example, the formula mass of NaCl is 58.44 amu, and its molar mass is 58.44 g/mol.

41. How do coordination compounds differ from other types of compounds?

Coordination compounds consist of a central metal atom or ion surrounded by ligands (molecules or ions that donate electron pairs). They have unique properties and structures compared to simple ionic or covalent compounds. For example, [Cu(NH3)4]2+ is a coordination compound where copper is the central metal ion and ammonia molecules are the ligands. These compounds are important in various fields, including catalysis and biological systems.

42. Why do some compounds change color when dissolved in different solvents?

Color changes in compounds when dissolved can be due to several factors, including changes in the compound's electronic structure, coordination with solvent molecules, or dissociation into ions. For example, copper sulfate appears blue in water due to the formation of [Cu(H2O)6]2+ complex ions, but it's colorless when anhydrous. This phenomenon is important in analytical chemistry and in understanding solvent effects on chemical species.

43. How does the concept of resonance contribute to the stability of certain compounds?

Resonance occurs when a molecule can be represented by multiple valid Lewis structures. The actual structure is a hybrid of these resonance forms, often resulting in greater stability than any single structure would suggest. For example, the benzene molecule's enhanced stability is explained by resonance between two equivalent structures, resulting in electron delocalization across the ring.

44. What is the significance of bond angle in determining molecular properties?

Bond angles are crucial in determining a molecule's shape, which in turn affects its polarity, reactivity, and other properties. They are influenced by factors like electron pair repulsion, bond order, and atomic size. For example, the 104.5° bond angle in water contributes to its bent shape and overall polarity, which is essential for its unique properties like high boiling point and ability to dissolve many substances.

45. How do intermolecular forces affect the physical properties of compounds?

Intermolecular forces (like hydrogen bonding, dipole-dipole interactions, and van der Waals forces) significantly influence a compound's physical properties such as boiling point, melting point, and solubility. Stronger intermolecular forces generally result in higher boiling and melting points. For instance, water's high boiling point compared to similarly sized molecules is due to strong hydrogen bonding between water molecules.

46. Why do some compounds conduct electricity in their molten state but not in their solid state?

This behavior is typical of ionic compounds. In the solid state, ions are fixed in position and cannot move freely, preventing electrical conduction. When melted, the ions become mobile and can carry an electric current. For example, solid sodium chloride (NaCl) is an insulator, but molten NaCl conducts electricity due to the movement of Na+ and Cl- ions.

47. What is the relationship between a compound's structure and its reactivity?

A compound's structure, including its molecular geometry, bond types, and electron distribution, directly influences its reactivity. For example, the presence of certain functional groups, like carbonyl groups in aldehydes and ketones, determines the types of reactions the compound can undergo. The strain in certain molecular structures, like cyclopropane, can also increase reactivity.

48. Why do some compounds form azeotropes, and what is their significance?

Azeotropes are mixtures of two or more liquids that maintain the same composition in the liquid and vapor phases when boiled. They form due to specific interactions between the components that result in a constant-boiling mixture. For example, a mixture of 95.6% ethanol and 4.4% water forms an