Topic 1 - Key concepts in chemistry Flashcards
What happens in chemical reactions?
Reactants are mixed together to form products
How did Democritus describe atoms in 500 BC?
Small spheres that are the smallest possible unit of matter that are separated from each other by empty space
What did John Dalton suggest in the 1800s about the atom?
He described them as solid spheres and suggested that the different types of atoms made up the different elements
What did J.J Thompson theorise?
He theorised that the atom consisted of a ball of positive charge with negatively charged electrons mixed throughout. This was called the plum pudding model
How did Rutherford develop the nuclear model?
He fired alpha particles at a thin sheet of gold foul. Most particles passed through but some were deflected off course. He theorised that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles. He developed a model of the atom with a central positive nucleus, surrounded by negative electrons
What was the issue with the nuclear model?
The atom should collapse because of the laws of attraction in that the electrons should be attracted to the nucleus, causing them to rush inwards causing the atom to collapse
How did Bohr fix the issue of the nuclear model?
He suggested that the electrons orbit the nucleus in energy shells that hold them in place and prevent the atom from collapsing
What did Chadwick discover in the central nucleus?
Neutral particles which he dubbed neutrons
What do we call an atom that has a charge?
An ion
What are isotopes?
Isotopes are atoms with the same atomic numbers / number of protons but different mass numbers / numbers of neutrons
What is the formula for relative atomic mass?
Ar = [(mass of isotope 1 x %abundance of isotope 1) + (mass of isotope 2 x %abundance of isotope 2)] all divided by 100
What is a molecule?
Something made from 2 or more atoms that are held together by chemical bonds
What does an oxygen molecule consist of?
2 atoms of oxygen held together by covalent bonds
What is a compound?
A substance made from 2 or more elements that are chemically bonded together
What is a mixture?
A substance containing 2 or more elements that are not chemically bonded
Is the air we breathe a compound or mixture?
A mixture
Is seawater a compound or mixture?
A mixture
What is the periodic table and what are the rows and columns called?
The periodic table is a table that displays all the known elements. Each row is called a period and each column is called a group
Do elements within a period show similar chemical properties?
No, elements in a group show similar chemical properties
What do elements in a group have in common?
They have the same number of electrons in their outer shell
How many electrons do elements in each of the groups have in their outer shell?
Group 1: 1
Group 2: 2
Group 3: 3
Group 4: 4
Group 5: 5
Group 6: 6
Group 7: 7
Group 0: 8
What is special about group 8?
They have a full outer shell of electrons, meaning they are stable and unreactive
How many electrons can the different electron shells hold?
The shell closest to the nucleus can hold 2 electrons and every other shell can hold 8
In a reaction will a group 1 element gain or lose an electron?
It will lose an electron because it “wants” to have a full outer shell of electrons
How are ions formed?
When an element reacts to lose or gain electrons to have a full outer shell, it no longer has a balanced charge; elements that gain electrons will have a negative charge and ions that lose electrons will have a positive charge
Write an equation for the ionisation of a magnesium atom
Mg -> Mg2+ +2e- or Mg2+ + 2e- -> Mg
What charge do elements in each of the groups have when they become ions?
Group 1 : +1
Group 2 : +2
Group 3 : +3
Group 4 : +4
Group 5 : -3
Group 6 : -2
Group 7 : -1
What groups do and don’t easily form ions and why?
Groups 1,2,6 and 7 form ions easily because they only need to gain or lose a small number of electrons so less energy is required and groups 5 and 6 don’t because they need to gain or lose a larger number of electrons so more energy is required
What ions do metal elements form?
Metal elements lose electron(s) from their outer shell when they react meaning they form a positive ion
Give 3 general properties of metals
They are good conductors of heat, sonorous and malleable
Why are metals strong?
Because they are held together by metallic bonds
What is a catalyst?
Something that can speed up a chemical reaction without being used up
What are transition metals?
Metals that share the same properties as metals that have their own section of the periodic table between groups 2 and 3
What is special about transition metals?
The metals can create ions of different charges and form different coloured solutions
How does ionic bonding work?
It is between a metal and a non-metal, the metal loses an electron(s) that is transferred to the non-metal so that they both have full outer shells
How do we draw a diagram of ionic bonding?
We can draw a dot and cross diagram
What do you have to remember when drawing dot and cross diagrams?
Surround the ion with square brackets and put the charge in the top right corner outside of the brackets
Why does ionic bonding work?
Because of the forces of attraction between the 2 ions and the weak forces of attraction between the metal’s electron and nucleus
What is an ionic structure?
A compound with many ions ionically bonded together and arranged to form a 3D structure known as a lattice
Give 3 properties of ionic compounds
High melting and boiling points, high strength bonds and the ability to conduct electricity when a liquid
Why can ionic compounds only conduct electricity in water?
The ions are free to move and carry charge
Why do ionic compounds have high melting and boiling points?
Because the bonds between the ions are strong and a lot of energy is needed to break them
How can potassium ions form an ionic compound with carbonate ions?
Potassium ions have a charge of 1+ and carbonate ions have a charge of 2-. This means that every carbonate ion will bond with 2 potassium ions
What are the ionic formulae for hydroxide, sulphate, nitrate, carbonate and ammonium?
Hydroxide: OH-
Sulphate: SO4 2-
Nitrate: NO3 -
Carbonate: CO3 2-
Ammonium: NH4 +
In covalent bonding are electrons shared or transferred?
They are shared
What atoms do covalent bonds form between?
Non-metallic atoms
How does the bonding for water work?
Before bonding, each hydrogen atom requires 1 more electron to complete its outer shell so wants to from 1 covalent bond and each oxygen atom requires 2 more electrons to complete its outer shell so wants to form 2 covalent bonds. This means that water is formed from 2 hydrogen atoms and 1 oxygen atom so they both have full outer shells
What is a simple covalent molecule?
A simple molecule has multiple atoms covalently bonded together. These bonds are very strong but the forces of attraction between the separate molecules are very weak, so simple molecules are easily separated from one another. This is why simple molecular structures have low melting and boiling points - the intermolecular forces only require a small amount of energy to break
What are giant covalent structures?
Covalent substances with millions of atoms
What state of matter are most simple covalent structures in at room temperature?
Gaseous
What are chlorine, bromine and iodine at room temperature?
Chlorine: gas
Bromine: liquid
Iodine: solid
Why are different halogens in different states at room temperatures?
They have different melting and boiling points; as you go down the group the atoms get bigger, meaning there will be more intermolecular forces so more energy and more temperature will be required to break them
Give 2 properties of simple molecular substances?
They are unable to conduct electricity and have low boiling points
How are the atoms in diamond and graphite arranged?
They are both giant covalent structures of carbon and the atoms are arranged in a regular repeating lattice structure with many multiple covalent bonds between each atom
Give a summary of giant covalent structures
Every atom is connected by strong covalent bonds, there are no weak intermolecular forces as there is only one structure, they have high melting and boiling points and cannot conduct electricity (except of graphite)
Give a summary of simple covalent structures
Strong covalent bonds between the atoms of each molecule, there are weak intermolecular forces between the molecules, they have low melting and boiling points and cannot conduct electricity
Give 3 properties of diamond
It is strong, has a high melting and boiling point and doesn’t conduct electricity
What is an allotrope?
2 substances made from the same element, that are in the same physical state but have different structures
What are diamond, graphite, graphene and fullerenes allotropes of?
Carbon
What is the bonding situation of each carbon atom in diamond?
Each carbon atom is bonded to 4 others
Why can diamonds not conduct electricity?
Because each carbon atom is bonded to 4 others so there are no free electrons to carry charge
How are carbon atoms bonded in graphite?
Each carbon atom is bonded to 3 others
How are the carbon atoms arranged in graphite?
They are arranged in 2D layers of repeating hexagons
Is graphite able to conduct electricity and why?
Graphite can conduct electricity because each carbon atom has 1 delocalised electron, which can move freely and conduct charge
Why is graphite softer than diamond?
The 2D layers of graphite stack on top of each other, with only weak intermolecular forces holding them together, meaning the layers can slide over each other making the graphite easier to break
What is graphene and can it conduct electricity?
Graphene is a single layer of graphite, which consists of carbon atoms arranged into flat hexagons. It can conduct electricity because each carbon atom has 1 delocalised electron
What shapes can graphene be folded into?
They can be folded into tubes and spheres, which are known as fullerenes
What are 2 uses of fullerenes in industry?
Delivery of medicines around the body and catalysts in chemical reactions
Why are fullerenes useful as catalysts?
They have a high surface area to volume ratio
What is the formula for Buckminster fullerene and what is special about Buckminster fullerene?
C60 - Buckminster fullerene was the first spherical fullerene produced
What feature do carbon nanotubes have that makes them useful in tennis rackets?
Their high strength to weight ratio
When is metallic bonding used?
When metal atoms bind to other metals
What happens to the electron loses to become a cation in metallic bonding?
They become delocalised and are shared across all the ions in the structure
Why are metals good conductors of electricity and heat?
In metallic bonding, the electrons are delocalised from the metal ion lattice meaning they can carry charge but also thermal energy. This means that metals can conduct electricity and heat
What is an alloy?
A metal combined with one or more other elements
Why do alloys have a higher strength than pure metals?
Because the atoms/ions of the different elements have different sizes. This disrupts the regular layered structure and means the layers can no longer slide over each other
What does the law of conservation of mass state?
No atoms are lost or made during a chemical reaction
What is a chemical change?
A rearrangement of the atoms in the reactants to form the products
Why is it harder to measure the mass of a gas than a solid or liquid?
Some of the gas can easily escape into the air
If a chemical reaction is carried out in a beaker on a balance and the mass of the products is less than that of the reactants, why could this be? (3 reasons)
One of the products was a gas and floated off, or some of the reactants may have been spilled or some gas from the air may have reacted with one of the reactants
What is relative atomic mass?
The average mass of all the isotopes of that element
What is the symbol for relative atomic mass?
Ar
What is the symbol for relative formula mass?
Mr
What is the formula that links mass, moles and Mr?
Mass = moles x Mr
What is the mass of 0.25 moles of carbon dioxide?
11g
How would you solve this question: “Calculate the mass of sodium oxide that can be made by completely burning 5.00g of sodium in oxygen”?
Write the balanced equation, find the moles of the known substance (moles = mass/Mr), find the moles of the unknown substance using the molar ratio from the balanced equation and finding the mass of the unknown substance (mass = moles x Mr)
What is the formula for finding concentration from mass and volume?
Concentration = mass/volume
How do you get from cm^3 to dm^3?
Divide by 1000; 1cm^3 = 0.001dm^3
What is the equation that links the volume of a gas to the number of moles of that gas?
volume (dm^3) = moles x 24
What is the molecular formula of a substance?
The molecular formula of a substance shows the actual number of atoms of each element present in a compound or molecule
What is the empirical formula of a substance?
The simplest whole number ratio of atoms of each element in a compound
How would you solve this question: “An unknown compound has an empirical formula CH3 and an Mr of 30, find the molecular formula”?
Find the Mr of the empirical formula, see how many times it goes into the Mr of the molecular formula and multiply all the numbers in the empirical formula by what you just found. (If the number is a decimal round it)
How would you solve this question: “A compound is found to contain x% sulfur and y% oxygen by weight”?
Assume the mass is 100g and convert percentages into grams. Convert these masses into moles. Divided both mole values by the smallest mole and round to the nearest number to find a ratio. Use the ratio to write out the empirical formula
What is a limiting reactant?
Something that entirely reacts and limits how much product can be formed
What does it mean for a reactant to be “in excess”?
It does not all react and has no effect on the amount of product formed
