C1 Keywords

Question 1

Atoms

Answer 1

All substances are made of tiny particles called atoms. Atoms consist of electrons surrounding a nucleus that contains protons and neutrons.

Question 2

Elements

Answer 2

An element is a substance that is made of only one sort of atom. There are about 100 different elements. These are shown in the periodic table, which is a chart with all the elements arranged in a particular way.

Question 3

Compounds

Answer 3

Compounds are chemicals made from atoms of different elements joined by chemical bonds. They can only be separated by a chemical reaction.

Question 4

Mixtures

Answer 4

A mixture is made from molecules of elements and compounds that are simply mixed together, without chemical bonds. Mixtures can be separated using techniques such as filtration, chromatography, evaporation and distillation.

Question 5

Protons

Answer 5

Protons and neutrons have the same mass, which is about 2,000 times larger than the mass of an electron. Protons and electrons have an electrical charge. This electrical charge is the same size for both, but protons are positive and electrons are negative.

Question 6

Neutrons

Answer 6

Neutrons have no electrical charge; they are neutral.

Question 7

Electrons

Answer 7

Electrons are contained in shells around the nucleus. The total number of electrons is always the same as the number of protons in the nucleus, as shown in the diagram below.

Question 8

Electron Configuration

Answer 8

The electrons in an atom occupy energy levels. These are also called shells. Each electron in an atom is found in a particular energy level. The lowest energy level (innermost shell) fills with electrons first. Each energy level can only hold a certain number of electrons before it becomes full. The first energy level can hold a maximum of two electrons, the second energy level a maximum of eight, and so on.

Question 9

Electron Shells

Answer 9

Electrons are arranged in different shells around the nucleus. The innermost shell - or lowest energy shell - is filled first. Each succeeding shell can only hold a certain number of electrons before it becomes full. The innermost shell can hold a maximum of two electrons, the second shell a maximum of eight, and so on.

Question 10

Subatomic Particles

Answer 10

Each atom consists of a nucleus containing protons and neutrons, with electrons arranged around it in energy levels.

Question 11

Periodic Table

Answer 11

There are more than 100 different elements. The periodic table is a chart showing all the elements arranged in a particular way. The vertical columns in the periodic table are called groups. Each group contains elements that have similar properties.

Question 12

Chemical Formula

Answer 12

The chemical formula of a compound tells you how many atoms of each element the molecule contains.

Question 13

Atomic Mass

Answer 13

The mass number of an atom is the total number of protons and neutrons it contains. The mass number of an atom is never smaller than the atomic number. It can be the same, but is usually bigger.

Question 14

Atomic Number

Answer 14

The atomic number of an atom is the number of protons it contains. All the atoms of a particular element have the same atomic number (number of protons). The atoms of different elements have different numbers of protons. For example, all oxygen atoms have 8 protons and all sodium atoms have 11 protons.

Question 15

Filtration

Answer 15

Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered: the sand stays behind in the filter paper (it becomes the residue) the water passes through the filter paper (it becomes the filtrate)

Question 16

Distillation

Answer 16

Simple distillation is a method for separating the solvent from a solution. For example, water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.

Question 17

Chromatography

Answer 17

Paper chromatography is a method for separating dissolved substances from one another. It is often used when the dissolved substances are coloured, such as inks, food colourings and plant dyes. It works because some of the coloured substances dissolve in the solvent used better than others, so they travel further up the paper.

Question 18

Charges

Answer 18

Both protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. The neutron is neutral.

Question 19

Evaporation

Answer 19

Evaporation is used to separate a soluble solid from a liquid. For example, copper sulfate is soluble in water – its crystals dissolve in water to form copper sulfate solution. During evaporation, the water evaporates away leaving solid copper sulfate crystals behind.

Question 20

Groups & Periods

Answer 20

All the different elements are arranged in a chart called the periodic table.

Here are the main features of the table:

• the horizontal rows are called periods
• the vertical columns are called groups
• elements in the same group are similar to each other
• the metals are on the left and the non-metals are on the right (hydrogen is a non-metal but is often put in the middle)
• the main groups are numbered from 1 to 7 going from left to right, and the last group on the right is Group 0
• the block in between Group 2 and Group 3 is where the transition metals are placed
• there are only two elements in Period 1 (hydrogen and helium)