SC1 - Structure of the Atom and the Periodic Table

Question 1

What did Dalton’s theory propose?

Answer 1

Dalton’s theory proposed that:

• all matter is made up of tiny hard particles called atoms
• atoms are tiny, hard spheres that cannot be broken down into smaller parts
• atoms cannot be created or destroyed
• the atoms in an element are all identical (but each element has its own type of atom)

Question 2

What are the relative charges of a proton, electron and neutron?

Answer 2

Proton - +1
Neutron - 0
Electron - -1

Question 3

What are the relative masses of protons, neutrons and electrons?

Answer 3

Protons - 1
Neutrons - 1
Electrons - 1/1835

Question 4

Describe the structure of an atom.

Answer 4

In the centre of an atom is the nucleus, made up of protons and neutrons. Around this nucleus are fast moving electrons, found in shells at different distances from the nucleus.

Question 5

How were the elements of the periodic table originally arranged?

Answer 5

They were originally arranged in terms of increasing mass number, however this caused issues as some elements were grouped with others that had very different properties causing some to be swapped around despite them now not being in increasing mass order.

Question 6

How are the elements in the periodic table arranged now?

Answer 6

Now, the elements in the periodic table are arranged by increasing atomic number, which means that all elements are grouped with others with similar properties.

Question 7

What is the mass number?

Answer 7

The mass number is the total number of protons and neutrons in an atom.

Question 8

What is the atomic number?

Answer 8

The atomic number is the number of protons an atom contains.

Question 9

What are isotopes?

Answer 9

Isotopes are forms of the same element which have a different mass number but the same atomic number due to a difference in the number of neutrons they contain.

Question 10

What is the relative atomic mass?

Answer 10

The relative atomic mass is the average mass of an atom of an element relative to an atom of carbon-12, taking into account all of its isotopes and their abundances.

Question 11

How do you calculate relative atomic mass?

Answer 11

Relative atomic mass = (isotope 1 x abundance) + (isotope 2 x abundance) / 100
(Note that there may be more than two isotopes given)
e.g. chlorine-35 has an abundance of 75%, chlorine-37 has an abundance of 25%

(35 x 75) + (37 x 25) / 100 = 35.5

Question 12

How is the periodic table organised?

Answer 12

• elements in a row or period are in order of increasing atomic number
• elements with similar properties are in the same column or group
• non-metals are in the right side of the table, metals are on the left

Question 13

Explain the iodine-tellurium pair reversal.

Answer 13

Mendeleev’s periodic table arranged elements in order of increasing mass number. Tellurium was placed before iodine as it had a lower mass number. However, it’s properties did not fit in with its group and neither did iodine’s, so they were switched. Now, the periodic table is organised by increasing atomic number, and since tellurium has a higher atomic number than iodine, it was placed after it, explaining why they had to be swapped.

Question 14

How many electrons are in each shell?

Answer 14

First shell - 2

All shells after that - up to 8

Question 15

What do the group and period numbers tell you about an element?

Answer 15

Group number - the number of electrons in the outer shell (e.g. group 1 elements have one atom in their outer shell)
Period number - the number of electron shells an atom has (e.g. elements in period 1 have 1 electron shell)