2. Atoms and Atomic Structure

Question 1

Democritus

Answer 1

• Greek philosopher
• believed all matter is made of very small indivisible particles
• he called these particles ‘atoms’

Question 2

Dalton’s Atomic Theory

Answer 2

1. All matter is made up of tiny indivisible particles called atoms
2. All atoms of a given element are identical and are different from atoms of other elements
3. Atoms of different elements combine in fixed whole number ratios to form chemical compounds
4. Atoms cannot be subdivided, created or detroyed
5. A chemical reaction involves a rearrangement of atoms

Question 3

The Law of Conservation of Mass - Lavoisier

Answer 3

• in a chemical reaction, matter is neither created nor destroyed

Question 4

Lavoisier vs Dalton

Answer 4

Dalton’s theory explained Lavoisiers theory as follows:

• if all matter is made up of tiny indivisible particles, called atoms, which cannot be subdivided, created or destroyed, then in a chemical reaction these atoms must only be rearranged. Therefore, matter is neither created nor destroyed and thus mass must be conserved

Question 5

The Law of Constant Composition - Proust

Answer 5

• any given compound is always made up of elements combined in the same proportion by mass

Question 6

Proust vs Dalton

Answer 6

• if a compond is formed by the combination of atoms in a fixed ratio
• then their proportions by mass must also be fixed

Question 7

Atom

Answer 7

• smallest particle of an element that retains all of the chemical properties of the element
• contains 3 subatomic particles: protons, neutrons + electrons
• each subatomic particle has specific characteristics within the highly organised atomic structure
• made up of a nucleus + extranuclear space
• the interaction between atoms accounts for the properties of matter

Question 8

Nucleus

Answer 8

• extremely small + very dense cluster of protons + neutrons in the centre of an atom
• positively charged
• contributes most of the weight of the atom
• positively charged protons that repel each other are tightly packed with the neutral neutrons that act as buffers between the protons

Question 9

Extranuclear space

Answer 9

• contains negatively charged electrons arranged in highly ordered orbitals maintained by the repulsive forces between electrons + the strong attractive forces between the electrons + positively charged nucleus

Question 10

Proton

Answer 10

• subatomic particle found in the nucleus
• has a charge of +1
• has mass of approximately 1 amu

Question 11

Neutron

Answer 11

• subatomic particle found in the nucleus
• has no charge
• has mass of approximately 1amu

Question 12

Electron

Answer 12

• subatomic particle found in the space surrounding the nucleus
• has a charge of -1
• has mass of approximately 0.0005amu

Question 13

Atomic number

Answer 13

• # protons in the nucleus of an atom
• written as subscript

Question 14

Mass number

Answer 14

• # protons + # neutrons in the nucleus of an atom

Question 15

Atomic weight

Answer 15

• the weighted average of the masses of the naturally occuring isotopes of an element
• measured in amu

Question 16

amu

Answer 16

• atomic mass unit
• the unit used to measure the mass of an elementary particle, and an atom
• 1amu = 1/12th the mass of a carbon atom with 6 protons and 6 neutrons = 1.6605 x 10^-24 grams

Question 17

Isotopes

Answer 17

• atoms with the same number of protons but different numbers of neutrons
• have the same chemical properties
• often have slightly different physical properties
• radioactive properties are different
• most elements occuring naturally are found as a mixture of isotopes in more or less constant ratio

Question 18

Monatomic elements

Answer 18

• exist as single atoms

Question 19

Diatomic elements

Answer 19

• exist in a molecule of 2 atoms
• O, H, N, F, Cl, Br, I

Question 20

Polyatomic elements

Answer 20

• exist in molecules of 3 or more atoms
• O, P, S, C