key concepts 2 Flashcards
ionic bonding, covalent bonding, types of substances
explain how ionic bonds are formed
- transfer of electrons
- when metal and non-metal react together the metal loses electrons to form a cation and the non-metal gains these electrons to form an anion
what is a cation and an anion
cation - positive ion
anion - negative ion
what are oppositely charged ions attracted to one another by
- electrostatic forces of attraction
- this attraction is called an ionic bond
what is an ion
an atom or group of atoms with a positive or negative charge
explain the formation of ions in ionic compounds from their atoms in groups 1 and 2
- group 1 and 2 are metals
- lose electrons to form positive ions
explain the formation of ions in ionic compounds from their atoms in groups 6 and 7
- non-metals
- gain electrons to form negative ions
why do elements in the groups form ions with the same charges
because elements in a group have the same number of outer electrons
so have to lose or gain the same number to get a full outer shell
when do anions and cations form
- anions form when atoms gain electrons (they have more electrons than protons)
- cations form when atoms lose electrons (they have more protons than electrons
how to know when to use -ide or -ate in the names of compounds
-ide = just contains 2 elements
-ate = contains 3 or more elements, one of which is oxygen
how to work out the formula of an ionic compound
- ionic compounds are made up of a positively charged part and a negatively charged part
- overall charge of any ionic compound is 0 so all the negative charges in the compound must balance all the positive charges
1. write out the formulas of the ions
2. the overall charge must be 0 so work out the ratio of the ions that gives an overall neutral charge
ex - 1.Ca 2+, NO3 -
2. to balance 2+ charge you need to NO3 - ions - the formula is Ca(NO3)2
what is the structure of an ionic compound
lattice structure
a) consisting of a regular arrangement of ions
b) held together by strong electrostatic forces (ionic bonds) between oppositely - charged ions
explain how a covalent bond is formed
- when a pair of electrons is shared between two atoms
what does covalent bonding result in the formation of
molecules
recall the typical size (order of magnitude) of atoms and small molecules
about 10 to the power of negative 10 m
explain the formation of hydrogen using a dot and cross diagram
- hydrogen atoms have one electron so need one more to complete the first shell
- can form a single covalent bond with another hydrogen atom to do this (h2)
explain the formation of hydrogen chloride using a dot and cross diagram
- both atoms only need one more electron to complete their outer shells
explain how water is formed using a dot and cross diagram
- in water molecules an oxygen atom shares a pair of electrons with two H atoms to form
- two single covalent bonds
explain how methane is formed using a dot and cross diagram
- carbon has four outer electrons
- it can form four covalent bonds with hydrogen atoms to fill up its outer shell
explain how oxygen is formed using a dot and cross diagram
- an oxygen atom need two more electrons co complete its outer shell
- in oxygen gas each oxygen atom forms a double covalent bond
( bond made of two shared electron pairs) with another oxygen atom
explain the formation of carbon dioxide using a dot and cross diagram
- carbon atom shares two pairs of electrons
- with two oxygen atoms
- to form two double covalent bonds
explain the properties of ionic compounds
a) high melting and boiling points due to strong attraction between ions
b) solid ionic compounds don’t conduct electricity as the ions can’t move however when an ionic compounds melts, the ions are free to move and will carry an electrical charge
explain why typical covalent, simple molecular compounds have low melting and boiling points
- only need to break the feeble intermolecular forces and not the covalent bonds
- so its low because the molecules are easily parted from each other
explain why typical covalent, simple molecular compounds are poor conductors of electricity
- don’t contain any free electrons or ions
what are graphite and diamond
- different forms of carbon
- examples of giant covalent substances
describe the structures of graphite
- 3 covalent bonds, creating sheets of carbon atoms arranged in hexagons
describe the structures of diamond
- four covalent bonds
- rigid lattice structure
why is graphite used to make electrodes and as a lubricant
- no covalent bonds between layers
- held together weakly so free to move over each other
- so its soft and slippery
why is diamond used in cutting tools
- rigid lattice structure making diamond really hard
why does diamond have a high melting point
strong covalent bonds take a lot of energy to break
explain the properties of fullerenes
- huge surface area = good catalyst
- can cage other molecules = can deliver drugs directly to cells in the body
- made up of carbon atoms in closed tubes or hollow balls
explain the properties of fullerenes like C60
- buckminsterfullerene = C60
- forms a hollow sphere
- made of hexagons and pentagons
- stable molecule that forms soft brownish-black crystals
explain the properties of the fullerene graphene
- one layer of graphite
- a sheet of carbon atoms joined in hexagons
- one atom thick so it’s two dimensional
what properties do giant covalent structures have
- high melting and boiling points as lots of energy is needed to break covalent bonds
- generally don’t conduct electricity
- no soluble in water
describe simple polymers using poly(ethane) as an example
- large molecules containing chains of carbon atoms
- formed when monomers join together
what are the properties of metals
- malleable
- can conduct electricity
explain why metals are malleable
- layers of atoms can slide over each other
explain why metals contain an electrical charge
- delocalised electrons carry electrical charge and thermal energy through the material
- so metals are good conductors of electricity and heat
describe the limitations of models - dot and cross
- don’t show size of atoms or ions or how they are arranged
describe the limitations of the ball and stick models
- no correct scales
make it looks like there are gaps between atoms
describe the limitations to two and three dimensional shapes
2D - shape of substance or size of atoms
3D - only show outer layer of substance
describe metals
- shiny solids
- high melting points
- high density
- good conductors of electricity
describe non-metals
- low boiling points
- poor conductors of electricity
During ionic bonding do the non metals gain or lose electrons
Non metals GAIN electrons
During ionic bonding do metals gain or lose electrons
Metals LOSE electrons
