GCSE Chemistry C4

What did John Dalton do?

He described atoms as solid spheres, and said that different spheres made up different elements

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What did J.J.Thomson conclude?

He concluded that atoms weren't solid spheres. His measurements of charge and mass showed an atom must contain even smaller, negatively charged particles-electrons- Plum Pudding Theory

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What did Ernest Rutherford do?

He conducted the gold foil experiment. They fired positively charged particles at an extremely thin sheet of gold

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How did this experiment disprove the plum pudding model?

From the plum pudding model, they were expecting most of the particles to be deflected by the positive 'pudding' that made up an atom. Instead, most particles passed through the gold atom

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What did Rutherford come up with?

The theory of the nuclear atom. There's a tiny, positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons

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What did Niels Bohr propose?

That all electrons were contained in shells/fixed orbits. His theory of atomic structure was supported by many experiments and it explained other scientists observations

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Nucleus in atoms?

It's in the middle of the atom. Contains protons and neutrons. Has positive charge because of protons. Almost the whole mass of the atom is concentrated in the nucleus

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Electrons in atoms?

Move around the nucleus in electron shells. Negatively charged. Tiny, but cover a lot of space. The volume of their orbits determines the size of the atom. Have virtually no mass

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Why do neutral atoms have no charge overall?

This is because they have the same number of protons as electrons. The charge on the electrons is the same size as the charge on the protons, but opposite-so they cancel out

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What does the mass number tell you?

Total number of protons and neutrons. It is always the biggest number. Is the relative atomic mass

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What does the atomic number tell you?

Number of protons (therefore number of electrons). Atoms of the same element have the same number of protons

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How do calculate the number of neutrons?

Mass number- atomic number

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What does the group an element belongs to represent?

The number of electrons it has in its outer shell. Groups are vertical columns

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What does the period an element belongs to represent?

Periods are horizontal rows. The period to which the element belongs to corresponds to the number of shells of electrons it has

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What is an isotope?

Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers

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What did Dobereiner do?

He put the list of elements into groups based on their chemical properties. He put the elements into groups of three, which he called triads. The middle element of each triad had a relative atomic mass that was the average of the other two

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What were the Newlands Octaves?

Newland noticed that every eigth element had similar properties, so he listen the known elements in rows of seven. Unfortunately the pattern broke down on the third row with transition metals messing it up

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Why was his work criticised?

His groups contained elements that didn't have similar properties. He mixed up metals and non-metals. He didn't leave any gaps for elements that hadn't been discovered yet

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What did Mendeleev do?

Mendeleev put the elements in order of atomic mass. He left gaps in order to keep elements with similar properties in the same vertical groups. The gaps predicted the properties of so far undiscovered elements

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Electronic Configuration?

2.8.8

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What is ionic bonding?

In ionic bonding. atoms gain or lose electrons to form charged particles which are then strongly attracted to one another, because of the opposite charges

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What do ionic bonds form?

They form between metals and non-metals and always produce giant ionic structure. The ions form a closely packed lattice arrangement. The ions are not free to move, so these compounds don't conduct electricity. Very strong chemical bonds between ions

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Why do magnesium oxide and sodium chloride have high melting and boiling points?

This is due to the very strong attraction between oppositely charges ions in the giant structure. To break the bonds you have to overcome these attractive forces- takes a lot of energy

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What are ions?

They are charged particles-they can be single atoms or groups of atoms. When atoms gain or lose electrons to form ions, they try to get a full outer shell

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What happens when metals and non-metals form ions?

Metals lose electrons to form positive ions. Non-metals gain electrons to form negative negative ions. When metals and non-metals combine, they form ionic bonds

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What is covalent bonding?

When non-metals atoms combine together they form covalent bonds by sharing pairs of electrons

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What do substances formed from covalent bonding have?

Simple Molecular structures.The atoms within the molecule are held together by very strong covalent bonds. The forces attraction between these molecules are very weak

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What is the result of these simple molecular substances having weak forces of attraction?

The melting and boiling points are very low, because the molecules are easily parted from each other. They don't conduct electricity because there are no free electrons or ions

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Group 1 metals?

Lithium. Sodium. Potassium. Rubidium. Caesium. Francium

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Group 1 metals reactivity?

As you go down Group 1, the alkali metals become more reactive-the outer electron is more easily lose, because is is further from the nucleus so less energy is needed to remove it

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Properties of Group 1 metals?

Low melting point and boiling point. Low density. Very soft

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What do alkali metals always form?

Ionic compounds, not covalent

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How do group 1 elements experience oxidation?

They lose an electron to form a 1+ ion with a stable electronic structure. The more reactive the metal, the more likely it is to lose an electron. Loss of electrons is oxidation

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What happens when group 1 metal react with water?

When lithium, sodium or potassium are put in water, they react vigorously. They move around the surface, fizzing furiously and produce hydrogen. The reactivity with water increases down the group. Sodium and potassium melt in the heat of the reaction

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What flame do the metals produce when heated?

Lithium-red. Sodium-yellow. Potassium-Lilac

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Group 7 halogens?

Fluorine. Chlorine. Bromine. Iodine. Astatine. 7 electrons in outer shell

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Group 7 halogens reaction?

As you go down group 7, the halogens become less reactive, there's less inclination to gain the extra electron to fill the outer shell when its further out from the nucleus

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Properties of Group 7 halogens?

Chlorine is a fairly reactive, poisonous, dense green gas. Bromine is a dense, poisonous, orange liquid. Iodine is a dark grey crystalline solid

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How do group 7 halogens experience reduction?

Halogens gain an electron to form a 1- ion with a stable electronic structure. Gain of electron is called reduction

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What do the halogens react with to form salts?

Alkali metals to form salts called 'metal halides'

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How are metals held together?

By metallic bonding. These special bonds allow the outer electrons of each atom to move freely. Creates a sea of declocalised electrons throughout the metal

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Why do metals have high melting and boiling points?

There's a strong attraction between the delocalised electrons and the closely packed ions-causing strong metallic bonding. A lot of energy is needed to break these bonds

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What is meant by metals being malleable and having high tensile strength?

Malleable means they are able to be hammered into a different shape. High tensile strength means the metals are strong and hard to break

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Why are metals good conductors of heat?

Due to the sea of delocalised electrons which move freely in metal, carrying electrical current

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What does the resistance in metals mean?

It means that whenever electricity flows through them, they heat up, and some of the electrical energy is wasted as heat

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What is a superconductor?

When the metals get cold enough, their resistance disappears completely. Without any resistance, none of the electrical energy is turned into heat, so none is wasted

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What can you make using superconducting wires?

Power cables that transmit electricity without any loss of power, Really strong electromagnets that don't need a constant power source. Electronic circuits that work very fast, because no resistance slows them down

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Why is it difficult to produce a superconductor?

Metals start superconducting at less than -265*. It is very hard and expensive to get to that temperature, which limits the use of superconductors

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Examples of transition metals and their compounds making catalysts?

Iron is the catalyst used in the Haber process for making ammonia. Nickel is useful for the hydrogenation of alkenes

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Why are the compounds of transition elements colourful?

Due to the transition metal ion they contain. E.g. iron(II) compounds are usually light green, iron (III) compounds are orange, copper compounds are blue

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What is thermal decomposition?

Thermal decomposition is when a substance breaks down into and least two other substances when heated

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Transition metal carbonates?

Transition metal carbonates break down on heating. Examples=copper carbonate, iron carbonate, zinc carbonate, manganese carbonate

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Thermal decomposition of transition metal carbonates?

They break down into a metal oxide and carbon dioxide. Usually results in a colour change

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What is a precipitate?

A precipitate reaction is where two solutions react and an insoluble solid forms in the solution

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Precipitation in transition metal compounds?

Some soluble transition metal compounds react with sodium hydroxide to form an insoluble hydroxide, which then precipitates out. Example= copper sulfate + sodium hydroxide = copper hydroxide + sodium sulfate

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Using precipitation to test for transition metal ions?

Some insoluble transition metal hydroxides have distinctive colours. Copper hydroxide is a blue solid. Iron (II) hydroxide is a grey/green solid. Iron (III) hydroxide is a orange/brown solid

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Where do we get water from?

Surface water: lakes, rivers- these sources start to run dry during the summer months. Ground water: aquifers- rocks that trap water underground

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Process of purifying water- Filtration?

A wire mesh screens out large twigs, and then gravel and sand beds filter out any other solid bits

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Process of purifying water- Sedimentation?

Iron sulfate or aluminium sulfate is added to the water, which makes fine particles clump together and settle at the bottom

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Process of purifying water- Chlorination?

Chlorine gas is bubbles through to kill harmful bacteria and other microbes

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Where do low levels of pollutants come from?

Nitrate residues from excess fertiliser in rivers and lakes. Nitrates prevent blood from carrying oxygen properly. Lead compounds from old pipes. Pesticide residue from spraying too near to rivers and lakes

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In dry countries, how is drinking water produced?

Sea water is distilled. Distillation needs a lot of energy, so it's really expensive and not practical for producing large quantities of fresh water

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How to test for sulfate ions in water?

Using barium chloride. Add dilute hydrochloric acid to test sample. Add 10 drops of barium chloride solution, If white precipitate is produced, sulfate ions are present in solution

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How to test for halide ions in water?

Using silver nitrate. Add dilute nitric acid to test sample. Add 10 drops of silver nitrate solution. If halide ions are present a precipitate will form. Chloride ions-white precipitate. Bromide ions- cream precipitate. Iodide ions- pale yellow

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GCSE Chemistry C4

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