Chemical Changes And Structure #3: Atomic Bonds Flashcards
What can atoms be joined together by?
Bonds
How is a molecule formed?
When two or more atoms join together
What happens when two or more of the same atoms join together?
They make a molecule of an element
What are diatomic molecules made up of?
Only 2 atoms
How many diatomic elements are there?
7
What are the 7 diatomic elements?
Oxygen, Fluorine, Chlorine, Nitrogen, Hydrogen, Iodine, Bromine
(Our Friend Claire Needs Her Irn Bru)
Why do atoms bond?
To achieve the most stable outer electron arrangement- a full outer shell
What is a covalent bond?
Two positive nuclei held together by their common attraction for the shared pair of negative electrons
What are covalent bonds usually formed between?
Two non-metal elements
How do you break a covalent bond?
You need a LOT of energy as they are very strong forces of attraction
How are double or triple bonds formed?
When two or three electrons join another 2 or 3 electrons to pair up
What is an example of chemical formula?
HCl or H20
What is an example of full structural formula?
H - Cl or H - O - H
How many dimensions do molecules exist in?
3
What does the shape of simple covalent molecules depend on?
The number and orientation of bonds around the central atom
How can we show the shape of a molecule?
By using perspective drawings
What is the perspective of a straight bond?
In the plane of the paper (flat)
What is the perspective of a wedge bond?
Coming towards you
What is the perspective of a dashed bond?
Going away from you
Linear molecules are bonded by…
1 straight bond
Angular molecules are bonded by…
Bonded by 2 straight bonds
Trigonal Pyramidal molecules are bonded by…
One straight, wedged, and dashed
Tetrahedral molecules are bonded by…
2 straight, 1 wedge, 1 dashed
How many atoms in a linear molecule?
2
How many atoms in an angular molecule?
3
How many atoms in a trigonal pyramidal molecule?
4
How many atoms in a tetrahedral molecule?
5
What do bonding diagrams do?
Give a simplified picture of an atom’s outer electron
How do you draw a bonding diagram?
Draw the element with its electrons, and have the electron pair(s) interlocking on one of the atom’s branches
What can covalent substances form?
Discrete molecular OR giant network substances
Discrete
Small or individual
How are covalent molecular structures held together?
By very weak forces of attraction (intermolecular) between molecules
What can covalent molecular substances be at room temp?
Solids, liquids, or gases
What happens when a covalent molecular compound melts or boils?
- The weak intermolecular forces are broken
- The strong covalent bonds are left in tact
Less energy required to melt or boil a covalent molecular compound =
Low melting and boiling points
What are the ONLY type of bonds that covalent networks have?
- covalent
- NO INTERMOLECULAR BONDS
What are covalent network structures held together by?
Strong covalent bonds
Lots of energy required to break the strong covalent bonds =
High melting and boiling points
2 Examples of covalent network substances
- Carbon in the form of diamond
- Silicon Dioxide
Why is diamond considered the hardest substance?
Because it is a giant network structure held together by many covalent bonds
What does the chemical formula or a covalent molecular substance give?
The number of atoms present in a molecule
What does the formula of a covalent network substance give?
The simplest ration of atoms in the substance
Example of covalent network formula
SiO2, for every silicon there 2 oxygen
What is valency? (KEY TERM)
The ability of atoms to combine with other atoms
What does an atom’s valency depend on?
How many out electrons an atom has, and so how many bonds it needs to make to achieve a full outer shell
What elements use Roman Numerals to indicate their valency?
Transition metals
What do Roman numerals indicate in a compound?
Indicates which valency is being used
Ionic bonding is between….
Metals and non-metals (OPPOSITES ATTRACT)
What is an ionic bond?
The electrostatic force of attraction between positive and negative ions
What is an ionic lattice?
A giant arrangement on ions held together by electrostatic attraction (aka ionic bonds)
Ionic bond is only found in… not…
Compounds, elements
Elements are only arranged in what structures?
Covalent network, Covalent molecular, NOT ionic lattices
What do ionic lattices consist of?
Millions of ions held together by ionic bonds
Why does it require a lot of energy to break ionic lattices?
Because of the very strong ionic bonds
Example of melting point of ionic lattice?
BaCl is 961°C
Ionic lattices have very high…
Melting and boiling points
Ionic compounds are always what?
Solid at room temperature
What does the formula of an ionic compound give?
The simplest ration of ions in the substance
What does ionic formulae show?
The charge on each of the ions
What is the relationship between the group number and the charge in the ion?
How many electrons it must gain/lose to achieve a full outer shell
What should the ionic formulae always equal to?
0, they should cancel eachother out
What is a group ion?
An ion which gains more than one type of atom, basically a molecule with a charge
ions can flow through…
Solutions
Electrons can flow through…
Anything that’s not a solution
Why can metals conduct electricity?
- The outer electrons of metal atoms are not attached to a particular atom. They are DELOCALISED
- Metals can conduct electricity because electrons can flow through them
What do the atoms share in a covalent bond?
A pair of electrons
What effect does the shared pair of electrons have on a covalent bond?
This means that the electrons are NOT free to move around and there is so conductivity of electricity
Why can’t non-metals conduct?
They don’t have charged particles which can move
What is the exception to non-metals being non-conductive?
Carbon in the form of graphite
Why can graphite conduct even though it’s a non-metal?
- It has a layered covalent network structure
- Each carbon atom only uses 3 electrons for bonding. The remaining electron is DELOCALISED over the whole structure
- This means that the electrons are free to move between the layers therefore graphite can conduct electricity because electrons flow through it
Do covalent compounds (solids, liquids, solutions) conduct?
No
Why do covalent compounds not conduct?
The electrons do not move
Ionic compounds do not conduct electricity in what state?
Solid
When can ionic compounds conduct?
When dissolved in water or molten
Why do solid ionic compounds not conduct?
Because the ions are not free to move in the ionic lattice structure
Why can ionic compounds dissolved in water conduct?
Because the lattice breaks
Why can ionic compounds in the molten state conduct?
The melting breaks down the lattice and allows the ions to move
What can be said about covalent substances that are insoluble in water?
They may dissolve in other substances
What don’t covalent network substances do?
Conduct
Ionic lattice in tact means…
No conduction
What are many ionic compounds?
Soluble in water
Why are many ionic compounds soluble in water?
As they dissolve, the lattice structure breaks up allowing water molecules to surround the separated ions
4 Key facts about covalent molecular
- solids, liquids, or gases at room temp
- when a covalent molecular compound melts or boils, weak intermolecular forces are broken
- strong covalent bonds stay in tact
- less energy to break = low melting + boiling points
3 key facts about covalent network
- exist as giant network structures held together by strong covalent bonds
- lots of energy required to break covalent bonds = high melting + boiling points
- eg; carbon in the form of diamond, silicon dioxide
5 key facts about ionic bonding
- between a metal and non - metal
- electrostatic force of attraction between positive and negative ions
- opposites attract
- ionic bonding is only found in compounds, not elements
- elements = molecular, network, magnetic etc…
