Topic 4: Atomic Structure - Subtopic 1: Atoms & Isotopes

Question 1

What is the difference in size between the atom and the nucleus?

Answer 1

Radius of nucleus is over 10,000 times smaller than whole atom but contains almost all the mass of atom

Question 2

What are the properties of the proton?

Answer 2

• In the nucleus
• +1 Charge
• Mass of 1

Question 3

What are the properties of the neutron?

Answer 3

• In the nucleus
• Charge of 0
• Mass of 1

Question 4

What are the properties of the electron?

Answer 4

• Orbiting the nucleus
• Charge of -1
• Mass of 1/2000 (Negligible)

Question 5

Describe energy levels

Answer 5

• Electrons orbit nucleus at different levels
• Certain number of electrons can occupy each energy level
• Higher the energy level, the further the distance

Question 6

Describe the number of electrons which can occupy in each level

Answer 6

1st Energy Level - 2 Electrons
2nd Energy Level - 8 Electrons
3rd Energy Level - 8 Electrons

Question 7

What happens when EM Radiation is absorbed by an electron?

Answer 7

Move to a higher energy level

Question 8

Why are dark coloured objects good absorbers of electrons?

Answer 8

Do not reflect energy that hits them

Question 9

What happens when an electron moves down from a higher to lower energy level?

Answer 9

When an electron moves down to a lower energy level (closer to the nucleus), it emits a wave of electromagnetic radiation. This is how all colors in the visible spectrum are produced.

Question 10

Why do electrons eventually move from higher to lower energy levels?

Answer 10

Electrons in higher energy levels are unstable. They will eventually return to their original, more stable energy level that is closer to the nucleus, emitting electromagnetic radiation in the process.

Question 11

What is the atomic number?

Answer 11

The number of protons in an atom (also called the proton number). The atomic number determines which element an atom is.

Question 12

How are elements arranged in the periodic table?

Answer 12

Elements in the periodic table are ordered by their atomic number.

Question 13

What is the relationship between atomic number and electrons in a neutral atom?

Answer 13

The atomic number is equal to the number of electrons in an atom because atoms have the same number of electrons and protons to have no overall charge.

Question 14

What is the mass number?

Answer 14

The total number of particles in the nucleus of an atom (protons + neutrons).

Question 15

How do you calculate the number of neutrons in an atom?

Answer 15

Number of Neutrons = Mass Number - Atomic Number

Question 16

Why aren’t electrons included in the mass number calculation?

Answer 16

Electrons have a tiny mass compared to neutrons and protons. Their mass is considered negligible when compared to the particles in the nucleus.

Question 17

What is nuclear notation?

Answer 17

The way of showing the mass number and atomic number of an atom by writing them with the atomic symbol. The mass number is written as a superscript and the atomic number as a subscript to the left of the element symbol.

Question 18

In nuclear notation, what does the top (superscript) number represent?

Answer 18

The mass number, which equals the total number of particles (protons and neutrons) in the nucleus.

Question 19

In nuclear notation, what does the bottom (subscript) number represent?

Answer 19

The atomic number, which equals the total number of protons in the nucleus.

Question 20

What is the atomic number of hydrogen?

Answer 20

1 (It has 1 proton)

Question 21

What is the atomic number of sodium?

Answer 21

11 (It has 11 protons)

Question 22

What is the atomic number of uranium?

Answer 22

92 (It has 92 protons)

Question 23

If a sodium atom has a mass number of 23 and an atomic number of 11, how many neutrons does it have?

Answer 23

12 neutrons (23 - 11 = 12)

Question 24

What are isotopes?

Answer 24

Atoms of the same element that have an equal number of protons but a different number of neutrons.

Question 25

Name the three isotopes of hydrogen.

Answer 25

Hydrogen (1 proton, 0 neutrons), Deuterium (1 proton, 1 neutron), and Tritium (1 proton, 2 neutrons).

Question 26

How common is Deuterium?

Answer 26

About 2 in every 10,000 Hydrogen atoms is Deuterium.

Question 27

How common is Tritium?

Answer 27

About 1 in every billion billion hydrogen atoms is Tritium.

Question 28

How do different isotopes of the same element affect chemical properties?

Answer 28

The number of neutrons does not affect the chemical properties of an atom, such as its charge, but only its mass.

Question 29

Why do neutrons only affect the mass of an atom?

Answer 29

Because neutrons have no charge but do have mass.

Question 30

Why is chlorine's mass number on the periodic table listed as 35.5?

Answer 30

Because chlorine has 2 isotopes (chlorine-35 and chlorine-37), with chlorine-35 being about three times more abundant than chlorine-37.

Question 31

What happens when electrons are knocked out from an atom?

Answer 31

When one or more electrons are removed from an atom, it becomes positively charged and is called a positive ion.

Question 32

What is an ion?

Answer 32

An ion is an atom or particle with a non-zero charge.

Question 33

What are three ways electrons can be removed from an atom?

Answer 33

1) Electrons can be removed by friction when objects are rubbed together 2) Electrons can absorb electromagnetic radiation and gain enough energy to leave the atom 3) From chemical reactions.

Question 34

Why are ions more chemically reactive than atoms?

Answer 34

Because of their positive charge.

Question 35

What is a model in scientific terms?

Answer 35

A model is a way of describing something in order to explain the way it behaves.

Question 36

Who was the first to describe the idea of atoms?

Answer 36

Greek and Indian philosophers, including the Greek philosopher Democritus.

Question 37

What does the Greek word 'atomos' mean?

Answer 37

Indivisible.

Question 38

Who discovered electrons?

Answer 38

Physicist Joseph John Thomson at the end of the 19th Century.

Question 39

Describe the Plum Pudding model of the atom.

Answer 39

The atom was thought to consist of negatively charged electrons (the 'plums') in a positively charged 'dough' or 'pudding'.

Question 40

Why was the Plum Pudding model replaced?

Answer 40

Experiments in 1909 (Rutherford's scattering experiment) produced results that could not be explained by the Plum Pudding model.

Question 41

Who conducted the alpha scattering experiment?

Answer 41

Physicist Ernest Rutherford instructed two of his students, Hans Geiger and Ernest Marsden, to carry out the experiment.

Question 42

What were the three main observations from the alpha scattering experiment?

Answer 42

1) Most alpha particles passed straight through the gold foil 2) Some alpha particles changed direction but continued through the foil 3) A few alpha particles bounced back off the gold foil.

Question 43

What conclusion was drawn from most alpha particles passing straight through the gold foil?

Answer 43

Most of the atom is empty space.

Question 44

What conclusion was drawn from some alpha particles being deflected?

Answer 44

The nucleus has a positive charge which repels the positively charged alpha particles.

Question 45

What conclusion was drawn from a few alpha particles bouncing back?

Answer 45

The nucleus contains most of the mass of the atom and it is very dense.

Question 46

Describe the nuclear model of the atom proposed by Rutherford.

Answer 46

In the nuclear model: 1) Nearly all of the mass of the atom is concentrated in the center (the nucleus) 2) The nucleus is positively charged 3) Negatively charged electrons orbit the nucleus at a distance.

Question 47

How did Niels Bohr improve the nuclear model in 1913?

Answer 47

He proposed that electrons orbit the nucleus at different specific distances called energy levels, with up to 2 electrons in the first level, and up to 8 in the second and third levels.

Question 48

Why was the Bohr model accepted over the nuclear model?

Answer 48

1) It explained findings from different experiments better 2) It explained absorption and emission of electromagnetic radiation 3) Theoretical calculations matched experimental results.

Question 49

Who discovered the proton and when?

Answer 49

Ernest Rutherford discovered that the nucleus contained positively charged particles he called protons.

Question 50

What is the elementary charge?

Answer 50

The amount of charge in a proton, which is the same as the charge of a Hydrogen nucleus.

Question 51

What is the origin of the word 'proton'?

Answer 51

'Proto' means original - protons are the original unit of positive charge.

Question 52

Who discovered the neutron and when?

Answer 52

James Chadwick proved the existence of neutrons in the nucleus in 1932.

Question 53

What are the properties of a neutron?

Answer 53

A neutron has a mass similar to the proton but has no charge - it is neutral.

Question 54

What charge does an alpha particle have?

Answer 54

An alpha particle has a charge of +2 (it has 2 protons and no electrons).

Question 55

Why did the Plum Pudding model need to be replaced?

Answer 55

The experimental results of the gold foil experiment could not be explained using the plum pudding model.