Question

1. Define chemistry and provide examples of matter 2. Characterize the 3 states of matter with respect to the definiteness or indefiniteness of shape and volume 3. Explain the difference between elements, compounds, and homogeneous and heterogeneous mixtures 4. Represent elements and compounds using chemical symbolism 5. Distinguish between atoms and molecules 6. Describe the difference between chemical and physical properties and changes.

Answer 1

1. Chemistry is a branch of Science that deals with the composition, structure and properties of substance and the various elementary forms of matter, the way the substance changes and reacts with the other substance. . Examples of matter are: atoms (Example- Helium atom), compound (ex- water, table salt) , person , paper etc.

2. Three states of matter are:

Solid- Definite shape and volume

Liquid- Definite volume but not definite shape

Gas- Neither definite shape nor definite volume

3. Difference between elements are compounds:

i) Element is made up of single type of atom while compound are made up of different type of elements in definite proportions.

ii) An element is represented by symbol while A compound is represented using its chemical formula that represents the symbols of its constituent elements and the number of atoms of each element in one molecule of the compound.

iii) Example of elements are Hydrogen (H), Oxygen (O), sodium (Na) etc

Examples of compounds are: Water (H2O) , Sodium Chloride (NaCl) , Sodium Carbonate (Na2CO3) etc.

iv) Elements can not be broken down into simple substances by chemical reactions while compounds can be broken down into simpler substances by chemical reactions.

v) There are about 117 elements that have been observed. These are classified into metals, non metals and metalloids.

There are limitless number of chemical compounds that can be created i.e molecular compounds, ionic compounds, intermetallic compounds and complexes.

Difference between homogeneous and heterogeneous mixture:

A homogeneous mixture has the same uniform appearance and composition throughout while the heterogeneous mixture consists of different substances and phases.

Particle sizes are different in the homogeneous and heterogeneous mixtures.

Examples of homogeneous mixture are: sugar solution, corn oil , vinegar et .

Examples of heterogeneous mixture are: sand in water, Tomato juice, clouds in air etc.

4. Symbol of elements: Each element is given its own chemical symbol like H for Hydrogen and O for Oxygen, Mg for magnesium. Every chemical symbol starts with a capital letter, with the second letter written in lower case.

In the case of compounds chemical formulae is written with the cross multiplication of the valencies of the atoms/ polyatomic ions wriiten in subscript. For example: H2O (valency of H is +1 and that of oxygen is -2 written as subscript by the cross multiplication). Other examples: CO, Na2CO3, NaCl, Li2O, BeCl2 etc.

5. Difference between atoms and molecules

i) Atoms exist independently while molecules are formed when two or more than two atoms are combined together.

ii) When simple atoms are combined together with varying numbers, then molecules of different properties can be formed, but when simple molecules are combined together, a product is formed.

iii) A molecule is usually to exist by itself but an atom is not stable by itself.

iv) There is no bonding between the atoms but there is bonding between the molecules.

v) Example:Nitrogen (N) is a atom while Nitrogen (N2) gas is a molecule.

6. Difference between physical and chemical changes and properties

i) In the chemical change there is changes in the composition of the substance while in the physical change there is a difference in the appearance, smell or simply display of a sample of matter without a change in composition.

ii) The physical properties are: lusture, malleability, density, viscosity , mass, volume.. Any change in these properties is referred to as physical change.

The chemical properties are: change in temperature, change in colour, formation of precipitate, formation of bubbles etc. Any change in these properties are referred to as chemical changes.

iii) Examples of chemical change: Rusting of Iron, Formation of gas, Spoiled egg etc.

Examples of physical change are: boiling, melting, freezing, dissolve sugar in water etc.