Combined Science Chemistry 1

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  • Created by: Lilyk30
  • Created on: 20-04-18 18:13
What is an atom?
The smallest part of an element that can exist
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What are compounds?
Substances formed that contain two or more elements chemically bonded in fixed proportions
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What do chemical reactions always involve?
The formation of one or more new substances and often involves a detctable energy change
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How can chemical reactions be represented?
By word equations or symbol equations
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What is a mixture?
Two or more elements or compounds not chemically bonded; the chemical properties of each mixture are unchanged
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How can mixtures be separated?
Physical processes: filtration, distillation, fractional distillation, crystillisation and chromatography
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What is filtration used for?
Used to separate soluble solids from insoluble solids
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What is crystillisation used for?
Used to obtain a soluble solid from from a solution
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What is distillation used for?
Used to obtain a solvent from a solution
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What is fractional distillation used for?
Used to separate mixtures in which the components have different boiling points
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What is chromatography used for?
Used to separate the different soluble, coloured components of a mixture
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What may new experimental evidence lead to?
A scientific model being changed or replaced
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What were atoms thought of before electrons were discovered?
Tiny spheres that could not be divided
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What did the discovery of the electrin lead to?
The plum pudding model; suggested that the atom is a ball of positive charge with negative electrons embedded in it
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What lead to the conclusion that the mass of an atom was concentrated at the centre?
The results from the alpha particle scattering experiment
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What did Bohr do?
Adapted the nuclear by suggesting that electrons orbit the nucleus at specific distances
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What lead to the proton?
Later experiments concluded that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each having the same amount of charge
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What did James Chadwick do?
Provided the evidence to show the existence of neutrons within the nucleus
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What are the relative electrical charges of the particles in atoms?
Proton: +1 Neutron: 0 Electron: -1
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Are the number of protons equal to the number of electrons?
Yes
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What is the atomic number?
The amount of protons in an atom of an element
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What is the radius of a typical atom?
0.1 nm (1 x 10^-10)
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What is the radius of a typical nucleus?
1 x 10^-14 m
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Where is most of an atoms mass held?
In the nucleus
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What are the relative masses of protons, neutrons and electrons?
Proton: 1, neutron: 1, electron: very small
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What is the mass number?
The sum of the protons and neutrons in an atom
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What are isotopes?
Atoms of the same element that have different numbers of neutrons
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What is the relative atomic mass of an element?
An average value that takes account of the abundance of the isotopes of the element
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How are the elements in the periodic table arranged?
In order of atomic number and so that elements with similar properties are in columns, known as groups
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What did scientists try to classify elements by before the discovery of protons?
In order of their atomic weights
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What was wrong with the early periodic tables?
They were incomplete and some elements were placed at inappropriate groups if the strict order of atomic weights was followed
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What did Mendeleev do for the periodic table?
Overcame some of the problems by leaving gaps for elements that he thought had not been discovered
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What filled the gaps in the periodic table?
The elements with properties predicted by Mendeleev
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What are elements that react to form positive ions?
Metals
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What are elements that react to form negative ions?
Non-metals
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Why are the Group 0 elements called noble gases?
Because they are unreactive and do not easily form molecules because their atoms have stable arrangements of electrons
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What happens to the boiling points of noble gases as they go down the group?
They increase with increasing relative atomic mass
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What are the Group 1 metals known as?
Alkali metals
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What happens in Group 1 as they go down the group?
The reactivity of the elements increases
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What are the Group 7 elements called?
The halogens
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What happens as you go down Group 7?
The higher the relative molecular mass and the lower the reactivity
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What is an ionic bond?
The bond between oppositely charged ions; metal and non metal
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What is a covalent bond?
The bond between a shared pair of electrons; non-metal and non-metal
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What is a metallic bond?
The particles are atoms which share delocalised electrons; metallic elements and alloys
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Explain ionic bonding
When a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal atom are transferred; metal atoms lose to become + ions; non-metals gain to become - ions
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What is an ionic compound?
A giant structure of ions
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What are ionic bonds held together by?
Strong electrostatic forces of attraction between oppositely charged ions
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Are covalent bonds strong?
Yes
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What do metals consist of?
Giant structures of atoms arranged in a regular pattern
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What is special about t he electrons in the outer shell of metal atoms?
They are delocalised and free to move through the whole structure
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What are the three states of matter?
Solid, liquid, gas
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What happens at the melting point?
Melting and freezing
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What happens at the boiling point?
Boiling and condensing
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What does the amount of energy needed for a substance to change state depend on?
The strength of the forces between the particles of the substance
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What are the limitations of the state of matter model?
There are no forces, all the particles represented as spheres and that the spheres are solid
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What are the properties of ionic compounds?
Regular structures; strong electrostatic forces of attraction; high melting and boiling points; when molten, can conduct electricity; not when solid
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What are the properties of small molecules?
Gases or liquids; low melting and boiling points; weak intermolecular forces; larger molecules have higher melting and boiling points; don't conduct electricity as molecules have no overall charge
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How are atoms in the polymer molecules linked together?
By strong covalent bonds
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Why are polymers solid at room temperature?
The intermolecular forces are quite strong
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What are giant covalent structures?
Solids with very high melting points
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How is the structure of giant covalent structures held together?
By strong covalent bonds
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Give examples of giant covalent structures
Diamond, graphite and silicon dioxide
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What are the properties of metals?
Strong metallic bonds; high melting and boiling points
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Why can pure metals be bent shaped?
The atoms are arranged in layers
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What are metal alloys?
Pure metals mixed with other metals
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Why are metals good conductors of electricity?
Because the delocalised electrons in the metal carry electrical charge through the metal
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Describe the structure of diamond
Each carbon atom forms four strong covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity
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Describe the structure of graphite
Each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers
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How many electrons from each carbon atom is delocalised?
One
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What is graphene?
A single layer of graphite and has properties that make it useful in electronics and composites
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What are fullerenes?
Molecules of carbon atoms with hollow shapes, based on hexagonal rings of carbon atoms
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What are carbon nanotubes?
Cylindrical fullerenes with very high length to diameter ratios
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What does the law of conservation of mass state?
No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the mass of the reactants
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What is the relative formula mass?
The sum of the relative atomic masses of the atoms in the numbers shown in the formula
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Why might some reactions appear to involve a change in mass?
Because a reactant or product is a gas and its mass has not been considered
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Whenever a measurement is made, what is there?
Uncertainty about the result obtained
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How are chemical amounts measured?
In moles
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What is the mass of one mole of a substance in grams numerically equal to?
Its relative formula mass
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What is the value of the avogadro constant?
6.02 x 10^23
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How can you use moles to balance equations?
Can be calculated from the masses of the reactants and products by converting the masses in grams to amounts in moles and converting that into whole number ratios
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What is common in a chemical reaction involving two reactants?
Use an excess of one of the reactants to ensure that all of the other reactant is used
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What is the limiting reactant?
The reactant that is completely used up because it limits the amount of products
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How is the concentration of a solution measured?
In mass per given volume of solution
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How are metal oxides produced?
When metals react with oxygen (oxidation reaction)
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What is an oxidation reaction?
The loss of oxygen
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What is a reduction reaction?
The gain of oxygen
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What is the reactivity of a metal related to?
Its tendancy to form positive ions
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How can metals less reactive than carbon be extracted from their oxides?
By reduction with carbon
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What do acids react with to produce salts and hydrogen?
Some metals
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How are acids neutralised?
By alkalis and bases to produce salts and water; by metal carbonates to produce salts, water and carbon dioxide
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How can soluble salts be made?
From acids by reacting them with solid insoluble substances; the solid is added to the acid until no more reacta and the excess solid is filtered off
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When do acids produce hydrogen ions?
In aqueous solutions
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What do aqueous solutions of alkalis contain?
Hydroxide ions
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What is the pH scale and how can it be measured?
A measure of acidity or alkalinity of a solution; can be measured using a universal indicator or pH probe
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What happens in neutralisation reactions?
Hydrogen ions react with hydroxide ions to produce water
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What makes a strong acid?
Completely ionised in aqueous solution
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What makes a weak acid?
Only partially ionised in aqueous solution
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What are compounds?

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Substances formed that contain two or more elements chemically bonded in fixed proportions

Card 3

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What do chemical reactions always involve?

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Card 4

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How can chemical reactions be represented?

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Card 5

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What is a mixture?

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CalPro

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Great Resource to use before you sit you final exam

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