Unit 1 - Chemical Bonding, atoms Ions and balancing equations T2 Flashcards
Atoms
Everything in the world is made up of atoms. The structure of the atom is what gives an element its chemical and physical properties.
Atoms build up
Electrons - negatively charged particles that spin around the positive centre of an atom in circles called energy levels. Their mass is so small that it is nearly zero.
Protons
Positively charged particles that are contained in the nucleus of the atom (the centre) they have a mass of 1 amu (atomic mass unit).
Neutrons
Particles with no charge that are also contained in the nucleus of the atom. They also have a mass of 1 amu.
Arrangement of periodic table.
Arranged in order of atomic number, horizontal rows are called periods and the vertical columns are called groups.
Elements with similar chemical properties are in the same group, and have the same no. of outside electrons.
Group 1 - alkali metals
Group 2 - alkali earth metals
Group 7 - halogens
Group 8 - noble gases.
Properties of main groups of elements
Group 1, alkali metals - soft metals with low densities that react rapidly with water, producing an alkaline solution and hydrogen gas.
Group 2, alkali earth metals - similar to group 1, slightly less reactive, hardened and denser than group 1.
The elements in group 7 are known as halogens. Fluorine and chlorine are gases. Bromine is one of only two liquid elements. Iodine is solid. They exist as diatomic molecules - they have two atoms in each molecule. As you go down the group the halogens become less reactive.
The elements in group 0 are known as noble gases. They are very unreactive and exist as individual atoms (monatomic).
Atomic numbers
Each element has its own atomic number. It tells you how many protons there are in the element . Since atoms are neutral they must have the same number of protons as electrons.
Electron arrangement
All electrons are arranged into energy levels. First energy level can hold two electrons, with the others being able to hold 8 (only true for first 20 elements)
Mass number
Mass number is protons + neutrons.
Isotopes
Atoms with the same atomic number but differing mass numbers.
This means that they will have different number of neutrons.
Relative atomic mass
Elements which form isotopes have relative atomic mass (RAM)
RAM of each element shown in the data book is calculated from the masses of all the isotopes of an element taking into account the percentage proportion of each. You can tell which isotope is more abundant if it is closer to the RAM.
Covalent bond
Shared pair of electrons between non metal elements. Aim is to give one another a full outer shell of electrons so that it is stable. Happens when two positive nuclei from different atoms are held together by their common attraction for the shared pair of electrons between them. Covalent bonds are strong bonds
Diatomic molecules
Iodine, Bromine, Chlorine, Fluorine, Oxygen, Nitrogen and Hydrogen.
Gen - u - ine.
Shape of molecules - tetrahedral.
Tetrahedral - four shared pairs of electrons, drawn with two lines, one dotted line and a triangle coming from the atom with valency of 4 to other atoms pointing in different directions. Example methane.
CH4
Valency
The no. of electrons an atom can share. Group 1 - V1 Group 2 - V2 Group 3 - V3 Group 4 - V4 Group 5 - V3 Group 6 - V2 Group 7 - V1 Group 8 - V0
Shape of molecules - Trigonal pyramidal
3 shared pair of electrons, drawn with one straight line, one dotted line and one triangle coming from the V3 atom to the other atoms. Example ammonia
NH3
Shape of molecules - angular
2 shared pairs of electrons. Drawn with two straight lines coming from the V2 atom to the other atoms. Example water H20
Shape of molecules double bond
When double or even triple bonds are shared draw bond with two lines rather than one.
Covalent Network
Covalent substances that are solids with high melting points have much larger molecules. A covalent network structure consists of a giant 3 dimensional lattice of covalently bonded atoms.
Examples of covalent networks are boron, carbon and silicon.
Carbon forms two structures diamond and graphite. Diamond is tetrahedral, graphite has a layered planar structure.
Ionic bonding
Ionic bonds are formed between a metal and a non metal for example sodium chloride. An atom of metal will lose an electron and form a positive ion. Metals form positive ions because they lose electrons to become stable. A non metal atom will gain an electron and form a positive ion
Ionic bond is the electrostatic force of attraction between a positively charged metal and a negatively charged ion.
Ionic compounds structure
Form a lattice structure, regular repeating arrangement of metal and non metal ions which creates compounds which conduct when molten or in solution but never when solid P. Can conduct as in those cases ions are free to move. Have high melting and boiling points due to the strong elctrostatic forces between them.
Dissolve in water easily.
Metallic bonding
In metallic npbonding the outer electrons are delocalised (free to move) this produces an electrostatic force of attraction between the positively charged metal ions and the negatively charged delocalised electrons.They generally have high melting points and boiling points however there is a great range in these melting and boiling points between metals. They conduct electricity due to their delocalised electrons which allow the flow of an electric charge through the metallic lattice. They can also be malleable and ductile.
Malleable
(of a metal or other material) able to be hammered or pressed into shape without breaking or cracking.
Ductile
(of a metal) able to be drawn out into a thin wire.
Electrolysis
Breaking up of an ionic solution using electricity..
Set up of electrolysis
Breaker containing ionic solution, has a D. C suppl with a negatively charged electrode and a positively charged electrode in it.
Electrolysis breakup
Solution is broken up because electricity is passed through the solution. Positive metal ions are attracted to the negative electrode, their receiving electrons to form normal metal.
Negatively charged non metals are attracted to the positive electrode, there the ions lose extra electrons to form normal non metal.
Equation for metal looks like ionic formula for metal + electrons needed ——> normal metal.
Non metal ionic formula——> normal non metal + electrons given away.
Ions
Atoms with same protons but different number of electrons.
Chemical formulae
Shows the number of atoms of each element in the compound.
Prefixes
Mono - one Di - two Tri - three Tetra - four Penta - five Hexa - six
Figuring out formula
Step one - write down the symbols of both the elements involved.
Be careful of group ions like phosphate - find in data booklet.
Step two - beneath each symbol, write its valency.
Step three - swap the valencies over.
Step four - if the valencies can be simplified, divide them both by the smaller of the two numbers. If one of the numbers is already one, then they cannot be divided and simplified any further.
Step five - write the formula. If group ion is there put it in brackets - (NO3)
Formula Using Roman Numerals
Some elements, particularly the transition metals, do not always have the same valency in their different compounds. The valency of these elements is usually given in roman numerals inside brackets.
Ionic Formula - charges need
Initially we work out the chemical formula of the compound using the SVSDF
method.
2. Using the valency of each element you add the charge of that element to the top right of the symbol.
A metal is always positively charged and the non-metal is negatively charged.
Balancing equations
- Write out unbalanced equation.
- Write all elements in equation under = sign and write no. of each on their represented side.
- Multiply compounds / elements to make equal and always add on to no. when a change has been made.
- Once equal rewrite equation.
