Definitions & practical Techniques

Question 1

Isotopes

Answer 1

Different forms of the same element. Same number of protons. Different number of neutrons. Same atomic number. Different mass numbers.

Question 2

Compounds

Answer 2

Substances formed from two or more elements, held together by chemical bonds. A chemical reaction is needed to form and to break these bonds. A compound formed from a metal and a non metal consists of ions. A compound formed from non metals is called a molecule

Question 3

Molecules

Answer 3

Two or more non metals bonded together (covalently). Non metal compounds consist of molecules

Question 4

Mixture

Answer 4

No chemical bond. Easier to separate the different elements within the mixture

Question 5

Chromatography

Answer 5

Separates dyes in ink. Draw a straight line in pencil on chromatography paper. Add a dot of multiple colours of ink along this line - make sure they are well spaced out. Place the paper (stationary phase) in the solvent (mobile phase) and put a lid on top of the container so the solvent doesn’t evaporate. The solvent will seep up the paper, carrying the ink with it. Each different dye in the ink will move up the paper at different rates so the dyes will separate out. Singular dot = pure substance. Multiple dots = mixture of dyes. Take the paper out of the container once the solvent has nearly reached the top so that the paper can dry. The end result is a pattern of spots called a chromatogram. Use a pencil line not a pen line otherwise the solvent will carry the ink of the pen as well

Question 6

Filtration

Answer 6

Separation technique for mixtures. Used if product is an insoluble solid that needs separating from a liquid reaction mixture. Put filter paper in funnel and rest funnel in a beaker. Pour reaction mixture. Solid left on filter paper.

Question 7

Evaporation

Answer 7

Separation technique for mixtures. If solid is soluble and in a liquid. Pour the solution into an evaporating dish. Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form. Keep heating the evaporating dish until all is left is dry crystals

Question 8

Crystallisation

Answer 8

Separation technique for mixtures. If the salt decomposes, evaporation cannot be used so crystallisation is used. Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated. Once some of the solvent has exasperated or you see some crystals start to form (the point of crystallisation), remove the dish from the heat and leave the solution to cool. The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution. Filter the crystals out of the solution and leave them in a warm place to dry.

Question 9

Simple distillation

Answer 9

Separation technique for mixtures that contain a liquid. Used for separating out a liquid from a solution. The solution is heated. The part of the solution with the lowest boiling point evaporates first. The vapour is then cooled in the condenser and condenses back into liquid form and is collected in a beaker. You can only use simple distillation to separate things with very different boiling points.

Question 10

Fractional distillation

Answer 10

Separation technique for a mixture of liquids with fairly similar boiling points. Put mixture in a flask and put a fractionating column on top of it. Make sure at the top of the fractionating column there is a bung with a thermometer going through. Heat the mixture. Due to the different boiling points, each liquid will evaporate at different temperatures. The liquid with the lowest boiling point evaporates first. Liquids with higher boiling points might start to evaporate as well but the top of the column is cooler so they will condense back into liquid form before reaching the top. The liquid with the lowest boiling points goes into the condenser which is surrounded by a water cooling jacket and condenses into liquid form and is collected in another beaker. This process is repeated for each boiling point of each substance.

Question 11

Electron shells

Answer 11

Lowest energy levels are filled up first - these are the innermost shell, nearest to the nucleus. 1st shell holds up to 2 electrons. The rest carry up to 8 electrons. Full outer shells are stable (noble gases). If the outer shell is not full, atoms are more likely to react so that they fill this shell. E.g. Electrons structure of sodium = 2, 8, 8, 5

Question 12

Metals

Answer 12

All have metallic bonding. Basic properties:

• strong
• malleable
• sonorous
• high melting and boiling points
• conduct heat and electricity

Question 13

Non metals

Answer 13

More dull looking
Brittle
Aren’t always solid at room temp
Lower density
Don’t generally conduct electricity

Question 14

Transition metals

Answer 14

Have the same properties as metals and some others:

• can have more than one ion
• Often coloured
• often make good catalysts

Question 15

Group 1 elements

Answer 15

Reactive, soft metals. Alkali metals. One electron in outer shell. Low density. Form +1 ions. Much less dense, strong and hard than transition metals. Lower melting points. React much more vigorously with water, oxygen and group 7 elements. Trends go down:

• increasing reactivity
• lower melting and boiling points
• higher relative atomic mass

Question 16

Group 1 elements reaction with water

Answer 16

React vigorously to produce hydrogen gas and metal hydroxides (compounds that dissolve in water to produce alkaline solutions). The more reactive (lower period), the more violent that the reaction is.
Amount of energy given out increase by going down the group.

Question 17

Group 1 elements reaction with chlorine

Answer 17

React vigorously when heated in chlorine gas to for, white metal chloride salts. Reactivity increases as you go down group so the reaction gets more vigorous

Question 18

Group 1 elements reaction with oxygen

Answer 18

React to form a metal oxide. Different types of oxide will form, depending on the group 1 metal. Reacting the oxygen is why group 1 metals tarnish in air, forming a full metal oxide layer.