ATOMIC STRUCTURE

Question 1

What is an atom?

Answer 1

An atom is the smallest particle of an element that can exist by itself and still have the same chemical properties as the element.

Question 2

What are the three different types of fundamental particles of an atom?

Answer 2

The subatomic particles of an atom include

Protons
Neutrons
Electrons

Question 3

Where are the protons, neutrons and electrons located in an atom?

Answer 3

Protons and neutrons are in a fixed position in the centre or nucleus of an atom. The electrons are found spinning around the nucleus in energy shells.

Question 4

What is the relative charge and relative mass of a proton, neutron and electron?

Answer 4

proton = +1 and 1
neutron = 0 and 1

electron = -1 and 1/1840

The number of protons and electrons are the same.

Atoms of different elements contain different numbers of protons and electrons - this is what makes the elements different.

Question 5

What is atomic number?

Answer 5

Atomic number (or proton number) is the number of protons in the nucleus of one atom of an element.

Since the number of electrons in an atom is always equal to the number of protons, the number of electrons in an atom is equal to the atomic number.

Question 6

What is mass number?

Answer 6

Mass number (or nucleon number) is the total number of protons and neutrons in the nucleus of one atom of an clement.

The number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number. More than one element can have the same mass number, so the number is not unique to a particular element.

Question 7

Nuclear notation?

Answer 7

An atom (or ion) of an element can be represented using the nuclear notation given below:
A
X
Z
where: X = atomic symbol A = mass number
Z = atomic number

a c
X
b d

a – mass number
c - charge
X – symbol of atom.
b – atomic number
d - number of items in the entity

Question 8

Energy shells?

Answer 8

Energy shells surrounding the nucleus contain electrons revolving at high speeds. The shells are relatively distant from the nucleus such that most of an atom is empty space. The electrons moving around the nucleus make up the volume of an atom.

Each energy shell is a specific distance from the nucleus. Electrons with the least energy occupy the energy shells closest to the nucleus. Electrons fill up the energy shells closest to the nucleus first. Each energy shell has a maximum number of electrons it can hold.

The first energy shell = two electrons.
The second energy shell = eight electrons.
The third energy shell = eight electrons.

Question 9

Electronic configuration?

Answer 9

The arrangement of electrons in an atom is known as its electronic configuration.

This can be represented in writing using numbers or by drawing a shell diagram.

Example
The helium atom
4
He
2
A helium atom has 2 protons and 2 neutrons (4 - 2) = 2 electrons.
The electronic configuration is 2
Therefore it has 2 electrons in the first shell.

The number and arrangement of electrons in an element determine its chemical properties, especially the number of electrons in the outermost energy shell which are known as the valence electrons.

Question 10

Can you define relative atomic mass?

Answer 10

Relative atomic mass (Ar) is the average mass of one atom of an element as compared to one-twelfth the mass of an atom of carbon-12.

Question 11

What are isotopes?

Answer 11

Isotopes are atoms of an element that have the same number of protons and electrons (same atomic number), but different number of neutrons (different mass number).

Question 12

Isotopes chemical properties, physical properties?

Answer 12

Isotopes of an element have the same chemical properties because the number and arrangement of electrons in them are the same. Isotopes of an element have slightly different physical properties because they have different numbers of neutrons which give them slightly different masses.

Question 13

What is half-life?

Answer 13

The time taken for half of the nuclei in a sample of a radioactive isotope to undergo radioactive decay.

Question 14

What are 5 uses of radioactive isotopes?

Answer 14

1. Carbon 14-Dating

The age of plant and animal remains can be determined. Living organisms constantly take in carbon from food molecules. It decays slowly in living organisms, and the amount lost is continually replenished as long as the organism takes in air or food. When an organism dies, it stops taking in carbon and the percentage of carbon-14 in its body decreases as it undergoes radioactive decay. By means of the half-life of carbon-14, the percentage of radioactive carbon-14 left in plant and animal remains is measured, it can be used to determine their ages.

2. Cancer Treatment

Cobalt-60 — cancerous cells in tumours can be destroyed by directing a controlled beam of radiation from radioactive cobalt-60 at the cells.

Radioactive iodine-131 — can be injected directly into the cancerous tumour to treat thyroid cancer.

3. Energy Generation

Uranium-235 — electricity is generated in nuclear power stations using radioactive uranium-235. If a uranium-235 atom is struck by a fast moving neutron, it splits into two smaller atoms. As it splits, two or three neutrons and a large amount of heat energy are released. The neutrons can then strike other atoms causing them to split and release more neutrons and energy. This causes a chain reaction which releases very large amounts of heat energy. If the chain reaction is controlled, the energy can be used to generate electricity. If the chain reaction is not controlled, a nuclear explosion (example, from an atom bomb) can occur.

4. Tracers

Radioactive iodine-131 can be used to check the functioning of the thyroid gland.

5. Heart Pacemakers

Batteries containing plutonium-238 should be able to power pacemakers for a patient’s lifetime without having to be replaced, since the half-life of plutonium-238 is about 87 years.