1c. Atomic Structure

Question 1

Atom

Answer 1

The smallest particles of an element that consists of electrons surrounding a nucleus that contains protons and neutrons

Question 2

Molecule

Answer 2

A group of two or more atoms chemically joined together forming an identifiable unit which retains the propertied and composition of the substance

Question 3

The Structure of the Atom

Answer 3

Elements are made of tiny particles of matter called atoms
Each atom is made of subatomic particles called protons, neutrons and electrons
Their size is so tiny that we can’t really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used
One relative atomic mass unit is equal to one twelfth the mass of a carbon-12 atom.
All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon.

Question 4

The Mass & Charge of Subatomic Particles

Answer 4

Proton:
- Relative Mass = 1
- Charge = +1

Neutron:
- Relative Mass = 1
- Charge = 0 (neutral)

Electron:
- Relative Mass = 1/1840
- Charge = -1

Question 5

Atomic Number

Answer 5

The number of protons in the nucleus of an atom

Question 6

Mass Number

Answer 6

The sun of the number of protons and neutrons in the nucleus of an atom

Question 7

Isotopes

Answer 7

Atoms of the same element contain the same number of protons and electrons but a different number of neutrons. Therefore, they have the same atomic number but a different mass number

Question 8

Relative Atomic Mass (Ar)

Answer 8

Weighted average mass of one atom of an element, taking into account the abundance of all the isotopes of that element . It is measured as a ratio 1/12 of the mass of an atom of carbon-12

Question 9

Deducing protons, neutrons & electrons

Answer 9

Finding the protons

The atomic number of an atom and ion determines which element it is
Therefore, all atoms and ions of the same element have the same number of protons (atomic number) in the nucleus
E.g. lithium has an atomic number of 3 (three protons) whereas beryllium has atomic number of 4 (4 protons)
The number of protons equals the atomic (proton) number
The number of protons of an unknown element can be calculated by using its mass number and number of neutrons:
Mass number = number of protons + number of neutrons

Number of protons = mass number – number of neutrons

Finding the electrons

An atom is neutral and therefore has the same number of protons and electrons
Finding the neutrons

The mass and atomic numbers can be used to find the number of neutrons in ions and atoms:
Number of neutrons = mass number – number of protons

Question 10

Calculate Relative Atomic Mass

Answer 10

The relative atomic mass of each element is calculated from the mass number and relative abundances of all the isotopes of a particular element
The steps below are to calculate the relative atomic mass
Start by finding out the mass of 100 atoms, then divide the result by 100 to get the Ar

Ar= (% of isotope A x mass of isotope A). + (% of isotope B x mass of isotope B) /100

The top line of the equation can be extended to include the number of different isotopes of a particular element present