Chapter 1: Classifying Substances And Exploring Atoms

Question 1

Changes of state

Answer 1

Changes from solid to liquid to gas and vice versa

Question 2

Properties of a solid

Answer 2

• Definite volume
• Has a definite shape or is made up of small pieces (crystals) that have definite shapes (sugar, salt, sand)
• Difficult to compress

Question 3

Properties of a liquid

Answer 3

• Definite volume
• Takes the shape of the container it is placed in
• Difficult to compress

Question 4

Properties of a gas

Answer 4

• Expands to fill the volume available to it
• Takes the shape of container it is placed in
• Easily compressed

Question 5

Homogenous substance

Answer 5

Of uniform composition throughout.

E.g. Pure water, sugar, aluminium, petrol, whisky, tap water, air

Question 6

Heterogenous substance

Answer 6

Having non-uniform composition where we can recognise small pieces of the material which are different from other pieces.

E.g. Strawberry jam, wood, iced water, fruit cake, concrete

Question 7

Impure substance

Answer 7

One substance contaminated with small amounts of one or more other substances.
An impure substance is therefore a mixture.

Question 8

Properties of a mixture

Answer 8

• Can be separated into two or more pure substances by physical/mechanical means (boiling, filtering etc.)
• May be homogenous or heterogeneous
• Displays properties of the pure substances making it up
• Has properties that can change as the relative amounts of the substances present are changed
• Has a variable composition
• E.g. Sea water, air, coffee, milk, petrol, whisky, brass, ‘silver’ coins

Question 9

Properties of a pure substance

Answer 9

• Cannot be separated into two or more substances by physical or mechanical means
• Is homogenous (crystals of sugar, piece of copper)
• Has properties such as appearance, colour, density, m.p. and b.p., which are constant throughout the whole sample
• Unchanging properties
• Has a fixed composition
• E.g. Table salt, sugar, copper, aluminium, diamond, gold, polyethylene and alcohol

Question 10

Element

Answer 10

• A pure substance which cannot be decomposed into simpler substances
• Only have one type of atom
• Constant physical and chemical properties

Question 11

Compound

Answer 11

• A pure substance which can be decomposed into simpler substances, for example into elements
• Always has elements present in the same ratio by mass
• Has different properties to the elements making it up
• E.g. Sodium chloride, sugar (sucrose), water

Question 12

Physical States of matter

Answer 12

Solids, liquids or gases

Question 13

Atom

Answer 13

• The smallest particle of an element which is still recognisable as that element
• Made up of subatomic particles

Question 14

Molecule

Answer 14

• Several atoms joined together (e.g. Water)

- The smallest particle of a substance that is capable of separate existence

Question 15

Diatomic molecule

Answer 15

• Pairs of atoms permanently stuck together to form a molecule
• All gaseous elements are diatomic, except for the noble gases

E.g. Oxygen gas, nitrogen gas, chlorine gas, hydrogen gas

Question 16

Separation of solids of different sizes

Answer 16

• Sieving separates mixtures in which the particles of the different substances have different sizes

E.g. Fine sand from coarser materials (gravel)

Question 17

Separating solids and liquids

Answer 17

Filtration - the liquid or solution passes through the paper while the suspended solid remains on top of the filter paper. The liquid or solution that passes through is called a filtrate (eg. Sand from seawater)
Sedimentation - the process in which solids settle to the bottom of the container (for coarse or very dense particles)
Decanting - the process of pouring off the liquid and leaving the solid at the bottom of the container (e.g. Tea off tea leaves)

Question 18

Separating dissolved solids in liquids

Answer 18

Vaporising - boiling or evaporating the solution
Evaporate to dryness - heating a solution in an evaporating basin to drive off all the solvent to obtain solid from solution (e.g. Salt from seawater)

Question 19

Distillation

Answer 19

• The process in which a solution or mixture of liquids is boiled with the vapour formed being condensed back to a liquid in a different part of the apparatus and so separated from the mixture
• Liquid collected from the distillation is the distillate

Question 20

Volatile

Answer 20

• Able to be converted to a vapour
• The more volatile of two liquids is the one with the lower boiling point
• If a mixture of a volatile liquid with non-volatile impurities is distilled, the distillate is pure liquid
• If a mixture of two liquids of comparable volatility is distilled, the distillate is generally richer in the more volatile liquid

Question 21

Fractional distillation

Answer 21

• Separates liquids by distillation when their boiling points are fairly close together
• Allows for repeated condensations and vaporisations up the column, effectively giving many separate distillations
• Pure sample of more volatile substance in the original mixture emerges from top of column
• E.g. Separation of crude oil into various commercial products,
  Separation of ethanol from fermented solutions

Question 22

Separating immiscible liquids

Answer 22

• Two liquids which, when mixed, don’t form a homogenous liquid, but instead stay as drops of one liquid dispersed through the other liquid. Eventually separate into two layers (e.g. Water and kerosene, water and cooking oil)
• Separated using separating funnel, which allows bottom liquid to run out without it getting contaminated by the top one

Question 23

Miscible liquids

Answer 23

• Form a homogenous liquid

- One liquid dissolves in another

Question 24

Separation based on solubility

Answer 24

• Separation of a mixture of solids
• Solvent added to dissolve soluble component; insoluble component filtered off
• Soluble solid recovered by evaporating filtrate to dryness
• E.g. Mixture of salt and sand

Question 25

Suspension

Answer 25

A dispersion of particles through a liquid with the particles being sufficiently large that they settle out on standing. A suspension is heterogenous. E.g. Sand in water

Question 26

Solution

Answer 26

A homogenous mixture in which the dispersed particles are so small that they never settle out and cannot be seen by a microscope. E.g. Salt or sugar in water, iodine in alcohol

Question 27

Nucleus of an atom

Answer 27

- Contains more than 99.95% of the mass of an atom, but its diameter is less than one ten-thousandth of the diameter of the whole atom - Contains protons and neutrons, and therefore carries a positive charge - Surrounded by electron cloud

Question 28

Electron

Answer 28

- Extremely small negatively charged particle with a mass of 1/2000 of the mass of a hydrogen atom - Move rapidly and randomly around nucleus - Do not move in fixed orbits; 'electron cloud' - Electrostatically attracted to nucleus; the closer they are, the stronger the force of attraction (this is why innermost shell fills first)

Question 29

Proton

Answer 29

Small positively charged particle having a mass approximately equal to the mass of a hydrogen atom and a charge equal in magnitude (but opposite in sign) to that of an electron

Question 30

Neutron

Answer 30

Small neutral particle which has the same mass as a proton

Question 31

Atomic number

Answer 31

- Z | - The number of protons in the nucleus of an atom of that element

Question 32

Mass number

Answer 32

- A | - The number of protons plus neutrons in the nucleus of an atom of the species concerned

Question 33

Isotopes

Answer 33

Atoms of one element that differ in the number of neutrons in their nuclei (e.g. chlorine-35 and chlorine-37). Chemical and physical properties of all isotopes of the one element are virtually identical.

Question 34

Relative atomic mass of an element

Answer 34

- Is the average mass of the atoms present in the naturally occurring element relative to the mass of an atom of the carbon-12 isotope taken as exactly 12.

Question 35

Physical changes

Answer 35

- A change in which no new substance is formed - Easily reversed, relatively small energy changes involved - Changing the state of a substance (melting lead, boiling water) - Changing physical appearance (grinding, rolling into sheets) - Dissolving solid in liquid (sugar in water) - Separating mixtures (filtering sand from water)

Question 36

Chemical change

Answer 36

- A change in which at least one new substance is formed - Also called chemical reactions - Difficult to reverse - Generally a large input or output of energy - E.g. Thermal decomposition, composition, corrosion, photo-reaction, reactions with oxygen or acid, combustion

Question 37

Evidence a chemical change has occurred?

Answer 37

- A gas is evolved (zinc granules in hydrochloric acid solution) - Precipitate is formed when two solutions are mixed (silver nitrate and sodium chloride forms silver chloride) - Change in colour - Significant change in temperature - Disappearance of a solid (which is not merely physical dissolution of the solid in a solvent) - An odour is produced

Question 38

Physical properties

Answer 38

- Properties of substances that relate to physical changes | - E.g. Melting and boiling points, appearance, density, electrical conductivity, hardness

Question 39

Chemical properties

Answer 39

- Properties that relate to chemical reactions substances undergo - E.g. Decomposition by heat, effect of light, reactivity with other substances such as oxygen

Question 40

Properties of Metals

Answer 40

- Solids at room temp. (excepting mercury) - Have a high metallic lustre - Good conductors of heat and electricity - Malleable (rolled into sheets) and ductile (drawn into wires) - Most have relatively high melting and boiling points - Fairly hard - Insoluble in water

Question 41

What are all elements trying to achieve?

Answer 41

All elements, except noble gases, tend to undergo chemical reactions and to form compounds in order to obtain the electron configuration of the nearby noble gases

Question 42

Valence electrons

Answer 42

- Electrons in the incompletely filled highest energy level (valence shell) - The electrons which participate in chemical reactions/bonds - Are lost, gained or shared so the element can achieve the nearest noble gas electron configuration

Question 43

Other methods of separation

Answer 43

Crystallisation - separates dissolved solid from liquid (different evaporating points) Gravity separation - solid from solid or liquid from liquid (different densities) Centrifuging - separates suspended solids (solids with higher densities sink to the bottom when spun) Magnetic separation - process of passing a mixture through a magnetic field to separate the magnetic and non-magnetic components Electrostatic separation - separates components which conduct electricity from those which cannot

Question 44

Properties of non-metals

Answer 44

- Gases, solids or liquids at room temp. - Non-conductors (except carbon) - Low melting and boiling points - Some are soluble in water - Dull - Brittle - Soft

Question 45

Properties of semi-metals

Answer 45

- Solid at room temp. - Semiconductors - Melting and boiling points vary (intermediate to high) - Insoluble in water - Generally shiny - Brittle and hard

Question 46

Transition metals (Group 3-12)

Answer 46

- Hard - High melting points - Properties of metals close together often very similar - Metals at the top are generally more reactive