Chapter 29 - Atomic Structure

Question 1

What is an atom?

Answer 1

The smallest particle of an element which still retains the properties of that element

Question 2

Who put forward the first theory about atoms, what did he believe and when was his theory disproved by a group of scientists?

Answer 2

John Dalton, and that they were tiny, round, hard and couldn’t be divided into anything smaller. This theory was disproved in the 1890s when a group of scientists began to explore atoms in more detail

Question 3

Name the three sub-atomic particles, their charge and when they were discovered

Answer 3

• the electron was discovered in 1897 (negative charge)
• the proton was discovered later (positive charge)
• the neutron w as discovered in 1932 (no charge - neutral)

Question 4

What unit of mass is used for sub-atomic particles, and why?

Answer 4

A.M.U. - Atomic Mass Unit

It’s used because the masses of these sub-atomic particles are too small for grams

Question 5

What is the mass of each of the three sub-atomic particles?

Answer 5

• neutron & proton = 1 a.m.u.

- electron = 1/1840 a.m.u.

Question 6

What type and amount of charge does each particle have, and where is each one situated?

Answer 6

• electron = charge of -1, situated outside the nucleus
• proton = charge of +1, situated inside the nucleus
• neutron = no charge, situated inside the nucleus

Question 7

What did Niels Bohr propose, and when?

Answer 7

That electrons move around the nucleus in fixed paths called orbits (shells), and in 1913

Question 8

What could the size of the nucleus in an atom be compared to?

Answer 8

Atom = Croke Park
Nucleus = Marble in the middle of the pitch
Electrons = Specks of dust in the stands
Everything else would be empty space in which the electrons are free to move

Question 9

What must equal what in an atom?

Answer 9

The number of protons = The number of electrons

This is because all atoms must be neutral

Question 10

What is atomic number?

Answer 10

The atomic number of an atoms is the number of protons in the nucleus of that atom

Question 11

How would you get the mass/ mass number of an atom? And why are electrons ignored?

Answer 11

Mass number = no. of protons + no. of neutrons

Electrons are ignored because they have such a small mass

Question 12

What is the shorthand method of showing the atomic number and mass number of an atom called, and why? Give an example.

Answer 12

The nuclear formula - it gives us information about the nucleus of the atom
27 (mass number)
Al
13 (atomic number)

Question 13

What information does the nuclear formula give us?

Answer 13

Position in the periodic table - atomic number = 13, meaning aluminium is the 13th element in the periodic table
No. of p + e - an = 13, meaning an atom of Al contains 13p + 13e
No. of p + n - mn of Al = 27, meaning the sum of p + n = 27
No. of neutrons - mn =27, 13p so 14n
In short; mn - an = no. of neutrons