Topic C1- Particles

Question 1

Name all 4 characteristics of a solid:

Answer 1

1) Strong forces of attraction between particles, which hold them in fixed positions in a very regular lattice arrangement.
2) The particles do not move from their positions, so solids keep a definite volume like liquids, but unlike liquids, they keep a definite shape.
3) The particles vibrate in their positions- the hotter a solid becomes, the more the particles vibrate (causing the solid to expand slightly when heated).
4) If you heat the solid (giving particles more kinetic energy), eventually the solid will melt and become liquid.

Question 2

Name all 4 characteristics of a liquid:

Answer 2

1) There is some force of attraction between the particles and they are free to move past each other but tend to stick together.
2) Liquids do not keep a definite shape and will flow to fill the shape of the container. They keep the same volume.
3) The particles are constantly moving in a random motion. The hotter the liquid, the faster they move. This causes liquids to expand slightly when heated.
4) Cooling a liquid will freeze it and it will become a solid, heating a liquid enough will evaporate it and it will become a gas.

Question 3

Name 4 characteristics of a gas:

Answer 3

1) There is no force of attraction between the particles- they are free to move; they travel in straight lines and only interact when they collide.
2) Gases don’t keep a definite shape or volume and will fill any container. When the particles bounce off the walls of the container, they exert pressure on the walls.
3) The particles move constantly with random motion. The hotter a gas gets, the faster they move. Gases either expand when heated or their pressure increases.
4) If you cool a gas, it will condense and become a liquid.

Question 4

Why is the particle theory not a perfect model for representing the 3 states of matter?

Answer 4

• The particles aren’t solid and they aren’t spheres- they are atoms, ions, or molecules.
• The model doesn’t give you an idea of the size of the particles, or the space between them.
• The model doesn’t show any forces between the particles, so there is no knowing how strong they are.

Question 5

What is physical change?

Answer 5

There are no new substances made- the original chemicals just change state. It is reversible.

Examples: change in size, state of matter, dissolving, freezing, boiling, melting, etc.

Question 6

What is chemical change?

Answer 6

During a chemical reaction, bonds between atoms from the substances you begin with (reactants) rearrange themselves to form different chemicals (products). Chemical change is irreversible.

Question 7

When did John Dalton create his theory? What was his theory?

Answer 7

• In 1803

- John Dalton described atoms as solid spheres and said that different spheres made up the different elements.

Question 8

When did J J Thomson release his atomic theory? What was the ‘plum pudding model?’

Answer 8

• In 1897
• J J Thomson concluded from his experiment that atoms weren’t solid spheres; his measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles- called electrons. The ‘solid sphere’ idea of atomic structure was changed, and the new theory was called the ‘plum pudding model’.

Question 9

When did Ernest Rutherford release his theory? How did he improve the ‘plum pudding model’?

Answer 9

• In 1909,
• Ernest Rutherford and his students conducted the famous gold foil experiment.
• They fired positively charged alpha particles at a very thin sheet of gold.
• From the plum pudding model, they were expecting the particles to pass straight through the sheet.
• This was because the positive charge of each atom was thought to be spaced out evenly, through the ‘pudding’ of the atom.
• Most particles went straight through, but some were deflected more than expected, and a small number were deflected backward.

-So the plum pudding model couldn’t be right.
Rutherford came up with the theory of the nuclear atom- there is a tiny, positively charged nucleus at the center of the atom, and it is surrounded by a ‘cloud’ of negative electrons.

-Most of the atoms consist of empty space.

Question 10

What is the Bohr model?

Answer 10

• Scientists realized that electrons in a ‘cloud’ around the nucleus of an atom, as Rutherford described, would be attracted to the nucleus, causing the atom to collapse.
• Niels Bohr proposed a new model of the atom where all the electrons were contained in shells.
• Bohr suggested that electrons can only exist in fixed orbits or shells, and not anywhere in between. Each shell had a fixed energy.
• His theory of atomic structure was supported by many experiments and it helped to explain lots of other scientists’ observations at the time. It is pretty close to the currently accepted version of the atom.

Question 11

Describe the properties of a proton:

Answer 11

• Protons have mass
• positively charged
• with a relative mass of 1
• and relative charge of +1.

Question 12

Describe the properties of a neutron:

Answer 12

• Neutrons have mass
• are neutral
• with a relative mass of 1
• and relative charge of 0.

Question 13

Describe the properties of an electron:

Answer 13

• Electrons have little to no mass
• are negatively charged
• with a relative mass of 0.0005
• relative charge of -1.

Question 14

What does the nucleus contain?

Answer 14

It contains protons and neutrons.

Question 15

What is the charge of the nucleus?

Answer 15

It has a positive charge because of the protons.

Question 16

How big is the nucleus?

Answer 16

Compared to the overall size of an atom, the nucleus is tiny- it has a radius of between about 10^-15m.

Question 17

Where are the electrons located?

Answer 17

Electrons move around the nucleus in electron orbitals

Question 18

How big is an atom?

Answer 18

The volume of the orbitals determines the size of an atom (atoms have the radius [called atomic radius] of about 10^-10m).

Question 19

What are molecules?

Answer 19

Molecules are made up of two or more atoms= they can be made of the same element or different elements.

Question 20

What are simple molecules?

Answer 20

Simple molecules are tiny- the bonds that form between these molecules are generally similar in length to the atomic radius- about 10^-10m.

Question 21

What are nanoparticles?

Answer 21

Nanoparticles are larger than simple molecules. They are typically made up of around 100 atoms and range from 1nm to 100nm in size.

Question 22

What is the atomic number?

Answer 22

The atomic (proton) number tells you how many protons there are.

Question 23

What is the mass number?

Answer 23

The mass number is the total number of protons and neutrons. The mass (nucleon) number is always the biggest number. On the periodic table, the mass number is actually the relative atomic mass.

Question 24

How do you calculate the number of neutrons?

Answer 24

To get the number of neutrons, just subtract the atomic number from the mass number.

Question 25

What is the charge of a neutral atom? Why?

Answer 25

Neutral atoms have no charge.

This is because they have the same number of protons as electrons. The charge from the elections is the same size as the charge on the protons, but opposite- so the charges cancel out. So, the number of electrons in a neutral atom is equal to the atomic number.

Question 26

How are ions formed?

Answer 26

Ions form when atoms (or groups of atoms) gain or lose electrons.

Question 27

When do negative ions form?

Answer 27

Negative ions form when atoms gain electrons- they have more electrons than protons.

Question 28

When do positive ions form?

Answer 28

Positive ions from when the atoms lose electrons- they have more protons than electrons.

Question 29

What are isotopes?

Answer 29

• Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons.
• Isotopes have the same atomic number but different mass numbers.
• If they had different atomic numbers, they would be different elements altogether.