WHAT ARE ATOMS LIKE?
Structure of an atom
all substances are made up of atoms. All atoms have a central nucleus. the nucleus is positively charged because it is made up of protons which are neutral. the nucleus is surrounded by negatively charged electrons. arranged in shells, over all an atom has no charge because it has the same number of protons as electrons.
Elements and compounds
an element is a substance that cannot be broken down. there are about 100 different kinds of element. A compound is a substance that contains at least two elements that are chemically combined. you can find out which elements make up a compound by looking at the compound formula.
an isotope is an atoms possible different atomic number, for example chlorine has two isotopes.
1. Chlorine, bromine and iodine are all in group 7 of the periodic table. they all react in similar ways, Explain why.
they are all in group 7 of the periodic table
2. How do you work out the number of neutrons in an atom?
mass number - atomic number
3. what us the electrical structure of phosphorus? (use a periodic table to help)
HOW ATOMS COMBINE - IONIC BONDING
When a metal and non metal combine electrons are transferred from one atom to the other to form ions, each of which has a complete outer shell. This can be as many electrons as is needed and can also use 3 atoms, e.g mg atom has two spare and Cl needs one so two Cl atoms are needed.
Formulae of ionic bonding
All ionic compounds are neutral substances that have equal charges on the positive ion(s) and negative ion(s). The table below shows how ions with different charges combine to form ionic compounds.
IONIC BONDING IS GIVING....
HOW ATOMS COMBINE - IONIC BONDING - Questions
1. What is an ion?
A positive or negatively charged molecule
2. How is a positive ion formed?
electrons are removed from the outer shell
3. how is a negative ion formed?
Electrons are added to the outer shell
4. Use your knowledge of the bonding that is used in magnesium chloride to predict some of its properties
- High melting point
- Very dense
COVALENT BONDING & THE PERIODIC TABLE
The periodic table
Groups are the vertical columns in the table of elements. Group one elements have 1 electron in the outer shell, group seven have 7 electrons in outer shell. Group eight elements have 8 electrons in their outer shell.
Periods are a horizontal row of elements in the periodic table this shows the amount of shells the electron has. Therefore elements in the third period have 3 shells of electrons around them.
Covalent bonding as where non metals combine by sharing the electrons rather than giving them. An example of covalently bonded molecules is Water. It is made up from 1 atom of oxygen and 2 atoms of hydrogen. Covalent bonding is used when both of the atoms used need electrons to complete their outer shell.
COVALENT BONDING & THE PERIODIC TABLE - Questions
1. what is a molecule?
two or more atoms bonded together.
2 why do simple covalently bonded molecules have low melting points and boiling points?
Because they have weak intermolecular forces.
3. they also have another characteristic in common. what is this and why does this happen?
they don't conduct electricity because they have no available electrons in their outer shell.
THE GROUP 1 ELEMENTS
The group one elements are called the alkali metals. They contain lithium, sodium, potassium, rubidium, caesium, France. Because they all are in group one, they have one electron in the outer shell. this also means they have similar properties.
They all react with water to produce hydroxide, they react in similar ways but as we go down the group they get more reactive and this means they react more vigorously with water. this is the equation for the reaction. Lithium can be replaced with any of the alkali metals.
LITHIUM + WATER = LITHIUM OXIDE + HYDROGEN
2Li + H20 = 2LiOH + H2
They all have similar chemical properties but as we go down the table the physical properties change. Generally the density increases as we go down the table (except for potassium). The melting points and boiling points decrease as we go down. Making Caesium have the lowest melting and boiling points and the highest density.
THE GROUP 1 ELEMENTS - Questions
1. Describe the main steps in carrying out a flame test.
A piece of nichrome is dipped in hydrochloric acid, to clean it. It is then dipped in the compound, the nichrome and the compound are then out in a flame and different colour flame is made for different compounds
2. What colour flame is made from the following compounds?
Potassium chloride - lilac
Lithium sulphate - Red
Sodium bromide - yellow
3. Write the equation for the formation of a sodium ion from a a sodium atom.
Na = Na (+) + e (-)
THE GROUP 7 ELEMENTS
The group of elements in group 7 of the periodic table are called the Halogens. They are all non-metals. being in group 7 they all have 7 electrons in the outer shell. this causes them to have similar chemical properties.
Halogens all react vigorously with alkali metals to form metal halides, for example.
LITHIUM + CHLORINE = LITHIUM CHLORIDE
2Li + Cl2 = 2LiCL
As we go down the group the halogens, unlike the alkali metals, get less reactive. This makes Fluorine the most reactive Halogen.
Unlike their chemical properties, that stay pretty much the same throughout the group, their physical properties differ greatly. The melting and boiling points increase as we go down the group as does the density.
THE GROUP 7 ELEMENTS - Questions
1. At room temperature what colour and what state are these elements?
- Fluorine? - Yellow gas
- Chlorine? - green gas
- Bromine? - orange liquid.
- Iodine? - grey solid
2. fill in this easy way to remember rules about oxidation and reduction?
- I s
- L oss of electrons
- sdjoa fdo
- R eduction
- I s
- G ain of electrons
Electrolysis is the name given to a chemical reaction that uses electricity. The electricity is then passed through a liquid or solution called an electrolyte e.g. copper (II) sulphate used to purify copper. Electrodes are used to connect to the electrolyte . The positive electrode (anode) is made of bolder (impure copper) and the negative electrode (cathode) is made of pure copper. It can also be used
Electrolysis of sulphuric acid
these are important equations of the electrolysis of sulphuric acid.
At the cathode this reaction takes place:
2H+ (aq) + 2e- = H2 (g)
At the anode this reaction takes place:
4OH- (aq) - 4e- = 2H2O (l) + O2 (g)
1. What product is made at the cathode when molten aluminium oxide is split by electrolysis. Oxygen is made at the anode.
2. What product is made at the anode when dilute sulphuric acid is split by electrolysis. Hydrogen is made at the cathode.
You can find the transition metals in the centre of the periodic table between groups 2 and 3. This section of the table contains metallic elements, such as Iron (Fe), Copper (Cu), Platinum (Pt), Mercury (Hg), Chromium (Cr), and Zinc (Zn).
THermal decomposition is a reaction where a substance is broken down into simpler substances by heating. When transition metal carbonates are heated, a colour change occurs and they decompose to form a metal and carbon dioxide. for example
Copper (II) carbonate (blue/green) = Copper (II) oxide (black) + carbon dioxide
TRANSITION METALS - Questions
1. What colour are these compounds of transition metals?
Copper compounds - Blue
Iron (II) compounds - Grey/green
Iron (III) compounds - orange/brown
2. what transition metals are used as catalysts in these chemical reactions?
Haber process - Iron
Making margarine - Nickle
METAL STRUCTURE AND PROPERTIES
Metal atoms are packed very close together in a regular arrangement. The atoms are held together by metallic bonds. They have high melting and boiling points because a lot of energy is needed to break the strong metallic bonds.
Metals are able to conduct electricity because the atoms are very close together and electrons can move between the atoms. At low temperatures, some metals can become superconductors, they have very little, or no resistance to the flow of electricity. This can be useful in when you need:
- a powerful electromagnet
- very fast electronic circuits
- power transmission that does not lose energy
METAL STRUCTURE AND PROPERTIES - Questions
1. List 5 properties of metals
- Lustrous (shiny)
- Hard and high density
- High tensile strength (able to bear loads)
- High melting and boiling points
- Good conductors of heat and electricity
2. why cant superconductors be used in everyday life?
because they only work at temperatures below -200 degrees C. This is a very low temperature and is impractical. But we are currently searching to find a superconductor that works at room temperature.