7 - bonding and structure Flashcards
Define ionic bond
The electrostatic attraction between 2 oppositely charged ions
What do ionic bonds form between?
A metal and a non-metal
How do you draw dot and cross diagrams for atoms?
Draw a circle for the nucleus and put the symbol of the element inside it
Don’t draw any rings
Draw the outer shell without a ring around the nucleus
Draw the electrons as crosses in one atom and as dots around the other element
Put electrons in spin pairs whenever possible
How do you draw ions as dot and cross diagrams and how do you draw their reaction?
Draw the metal nucleus with no electrons on the outside (all been taken)
Put square brackets around it and put the charge as a superscript to the brackets
Draw the non-metal nucleus with the outer electrons of the atom as crosses and the added electrons (from the metal) as dots
Put electrons in spin pairs
Put brackets around the non-metal ion etc. as well
If you need more than one of an ion, but a big number before the brackets
What is the charge of the ions in each of the groups?
Group 1 have +
Group 2 have 2+
Group 13 have 3+ except for boron (a non-metal)
Group 14 doesn’t form ions
Only the non-metals in group 15 form 3-
Only the non-metals in group 16 form 2-
Group 17 have -
Group 18 don’t form ions because they are noble gases
Define giant ionic lattice
A 3D structure of oppositely charged ions, held together by strong ionic bonds
What are the 2 main properties of ionic compounds?
Conduct electricity when molten or liquid
High melting and boiling points
Exist as giant ionic lattices
Why do ionic compounds conduct electricity as liquid or molten?
When you melt or boil, you pull apart ionic bonds
Allowing the ions (charged particles) to move and so they can carry a current
As a solid, the ions aren’t free to move so current isn’t carried
Why do ionic compounds have high melting and boiling points?
Very strong electrostatic attractions between oppositely charged ions so a large energy is needed to pull them apart
What effect does the charges of ions have on the ionic bonds?
A bond made by higher charges is harder to overcome
Requires more energy to overcome
What is a polar solvent?
A solvent which has slight negative and positive charges
What is the most common polar solvent?
water
How are ionic compounds and polar solvents linked?
Ionic compounds dissolve in polar solvents
Why do ionic compounds dissolve in polar solvents?
The ions of the compound are attracted to the small positive and negative charges of the polar solvent
What are metallic bonds?
Strong electrostatic attractions between positive metal ions and delocalised electrons
What is a giant metallic lattice?
The 3D structure of positive metal ions and delocalised electrons which are bonded by strong metallic bonds
Where do the delocalised electrons in metals come from?
Electrons leave the outer shells of metal atoms so that they are free to move about the structure
The loss of electrons from the metal atoms makes them positive metal ions
What are the 8 properties of metals?
Conduct electricity and heat
Malleable
Ductile
Strong
High melting and boiling points
Sonorous
Shiny
Not soluble in water
Why do metals conduct electricity and heat?
The free, delocalised electrons can carry the current through the structure
What do malleable and ductile mean?
Malleable means that it can be compressed without breaking
Ductile means it can be stretched / pulled out without breaking
Why do metals have high melting and boiling points?
The strong metallic bonds require a large amount of energy (and high temperature) to overcome
What does sonorous mean?
It makes a ringing noise when hit
define covalent bond
What is a covalent bond?
When does covalent bonding occur and why?
Reactions between 2 non-metals
So that all atoms have a full outer shell
What are the 2 ways of drawing covalent bonds?
The symbols for the atoms with lines between them to represent a shared pair
Dot and cross diagrams showing shared pairs between bonded atoms
What is a bonded pair?
A pair of electrons which is shared between 2 atoms
What is a lone pair?
An outer shell pair of electrons which is not involved in covalent bonding
What is a multiple covalent bond?
When there are more than 1 shared pairs of electrons between 2 atoms
How are multiple covalent bonds shown in each type of covalent diagram?
Multiple lines between atoms for simple diagram
Multiple shared pairs between atoms on dot and cross diagram
What are dative covalent bonds?
A shared pair of electrons which has been provided by one of bonding atoms only
What do dative covalent bonds usually form between
A lone pair is shared between its originator and a H+ ion (proton) usually
What is the other word for dative covalent bond?
Coordinate bonds
How do you draw dative covalent bonds in dot and cross diagrams?
Draw the pair as 2 dots or 2 crosses
If there are 2 bonded pairs around a central atom, what shape is formed and what is it called?
A linear shape
The electron pairs go on to the opposite sides of the central atom forming a straight line
The bond angle is 180 degrees
What is the shape called when there are 3 bonded pairs and what does it look like?
The shape is trigonal planar
The 3 bonds are on a flat plane
120 degrees bond angle
What is the shape for 4 pairs?
3D Tetrahedral shape
Bond angle is 109.5 degrees
What is the shape for 6 pairs?
Octahedral shape
Bond angle is 90 degrees
What determines the shape of a molecule?
The electron pairs surrounding a central atom
Why do the electron pairs surrounding a central atom form the shapes they do?
Each electron pair repels other electron pairs
The pairs push apart as much as possible
What is strange about beryllium?
Beryllium forms covalent bonds even though it’s a metal
E.g BeCl~2