C4 - ATOMS
1) It contains protons (positive charge) and
neutrons (neutral charge).
2) It has a positive charge because of the neutrons.
3) Almost the whole mass of the atom is
concentrated in the nucleus- both protons and
neutrons are heavy.
1) Move around the nucleus in shells.
2) Negatively charged.
3) They're tiny and have virtually no mass, but cover a lot of space.
It's the number of protons in an atom that defines what element it is. Elements all have different properties because of their difference in atomic structure.
The number of protons ALWAYS equals the number of electrons in a neutral atom.
The number of neutrons isn't fixed but is usally about the same number of protons.
C4 - LINE SPECTRUMS
When some elements are heated they produce flames with a distinctive colour. Lithium, sodium and potassium all produce coloured flames.
These colours help chemists identify a metal in a compound.
- When heated, the electrons in an atom become excited and release energy as light.
- The wavelengths emitted can be recorded as a line spectrum.
- Different elements produce different line spectrums because they emit different wavelengths of light due to each element having a different electron arrangement.
- This means line spectrums can be used to identify new elements.
The practical technique is called spectroscopy.
C4 - DEVELOPMENT OF THE PERIODIC TABLE
Döberiner and triads
In the 1800's the only thing they could measure was relative atomic mass.
In 1828 Döberiner put elements in groups according to their chemical properties. They were places into groups of 3 which he called triads.
The middle element of each triad had a relative atomic mass that was the average of the other 2.
Newlands' Law of octaves
Newlands noticed that when the elements are arranged in order of relative atomic mass, every eighth element had similar propeties, so he listed some of the known elements into seven:
BUT, the pattern broke down on the third row due to transition metals, he didn't leave any gaps for new elements and his group contained elements that didn't have similar properties.
Mendeleev put the elements in order of atomic mass, but left gaps so that elements with similar properties stayed in the same vertical groups.
The gaps were clever because they predicted the properties of the undiscovered elements. When they were found they fitted the pattern.
C4 - THE MODERN PERIODIC TABLE
In the periodic table the elements are laid out in order of increasing proton number. This arrangement means there are repeating patterns in the properties of elements.
1) Elements with similar properties form vertical columns- groups.
2) The group number tells you how many electrons there are in the outer shell.
3) If you know the properties of 1 element you can predict the properties of other elements in the group, e.g. reactivity.
4) In group 1 the elements react more vigorously as you go down the group.
5) In group 7 the elements reactivity decreases as you go down the group.
6) The rows are called periods.
The periodic table tells you:
1) The proton number of each element (and consquently
the number of electrons the element has).
2) The relative atomic mass of each element = the
total number of protons and neutrons that are in the nucleus. You can calcuate the number of neutrons in the atom by subracting the relative atomic mass number from the proton number.
C4 - ELECTRON SHELLS
1) Electrons always occupy shells/low energy levels.
2) The first shell can only take 2 electrons; the second shell can take 8 and the third shell can take 8.
3) Atoms are much happier when they have full electron shells.
5) In most atoms the outer shell is not full which makes the atom want to react.
6) An element's electron arrangement determines its chemical properties.
The first shell can only take 2 electrons and the second 8. So the electron configuration for nitrogen would be 2.5 because it has 7 electrons.
2 in the first shell; 5 in the second = 7 electrons.
C4 - IONIC BONDING
Ions are made when atoms lose or gain electrons.
When atoms lose or gain electrons they become charged particles called ions.
Ions can be made from single atoms or groups of atoms.
The aim of losing or gaining electrons is for the atoms to fill their outer shell.
WHEN ATOMS HAVE 1 ELECTRON IN THEIR OUTER SHELL- GROUP 1. THEY WANT TO GET RID OF THAT ELECTRON BY REACTING. WHEN THE ATOM LOSES THE 1 ELECTRON IT FORMS A POSITIVE ION.
WHEN ATOMS HAVE AN ALMOST FULL OUTER SHELL- GROUP 7. THEY WANT TO GAIN AN EXTRA ELECTRON TO FILL THEIR OUTER SHELL BY REACTING. WHEN THE ATOM GAINS AN ELECTRON IS BECOMES A POSITIVE ION.
Oppositely charged ions are attracted to each other. When a ion has a positive charge they stick to each other like glue- forming an ionic bond.
Compounds formed between Group 1 and Group 7 elements are held together by ionic bonds- ionic compounds.
C4 - IONS AND FORMULAS
Solid ionic compounds (sodium chloride) are made up of a giant latice of ions. Each lattice forms a giant crystal. When ionic compounds become molten or dissolved in water they can conduct electricity because the ions are able to move.
Different ions have different charges. Some metals can form ions with different charges. The number in the brackets after the name tells you the size of the positive charge. E.g. Iron (III) = Iron3+
In compounds the total charge must equal zero.
If ions in a compound have the same charge then they balance each other out. E.g. Li+ and F- balance out to form LiF because the + and - charge cancel each other out.
If the ions have differenct size charges, numbers need to be inserted to balance it. E.g. Ca2+ and Cl- needs 2 chlorine ions for every one calcium ion to balance it. Becoming CaCl2.
C4 - GROUP 1
Group 1 - The 'Alkali Metals'
- All have 1 electron in the outer shell - very reactive with similar properties.
- When the alkali metals react they form similar compounds.
- The alkali metals are shiny when freshly cut but rapidly react with oxygen in moist air and tarnish.
As you go DOWN group 1, the alkali metals:
1) BECOME MORE REACTIVE- The electron is lost easier because
it's further away from the nucleus.
2) HAVE A HIGH DENSITY- The atoms have more mass.
3) HAVE A LOWER MELTING POINT
4) HAVE A LOWER BOILING POINT.
When lithium, sodium or potassium are put in water they move aound the surface fizzing furiously. They produce hydrogen and potassium gets hot enough to ignite it. If not a lighted splint will indicate hydrogen by producing the "squeaky pop" as it ignites.
The reaction makes an alkaline solution.
Alkali metals react vigorously with chlorine producing colourless crystalline salts.
C4 - GROUP 7
Group 7 - The 'Halogens'
- All have 7 electrons in the outer shell- very reactive and similar properties meaning they form similar compounds.
- Halogens form diatomic molecules which are pairs of atoms.
As you go DOWN group 7, the halogens:
1) BECOME LESS REACTIVE- The outer electrons are
further from the nucleus and don't attract as strongly.
2) HAVE A HIGHER MELTING POINT.
3) HAVE A HIGHER BOILING POINT.
4) GO FROM GASES TO SOLIDS DOWN THE GROUP.
The halogens are all non-metals with coloured vapours at room temp.
Flourine- yellow gas. Chlorine- dense green gas. Bromine- orange gas. Iodine- dark grey crystalline solid/purple vapour.
The halogens react with alkali metals to form salts called metal halides.
They react with iron to form coloured solids called iron halides.
They cause a displacement reaction- where a more reactive element pushes out (displaces) a less reactive element from a coumpound.