Bonding, Structure and the properties of matter Flashcards
Ionic, covalent, metallic bonding, polymers, diagrams, formulae, particle model,
What are the three types of chemical bond?
-Ionic
-Covalent
-Metallic
What are the particles in ionic bonding?
Oppositely charged ions
What are the particles in covalent bonding?
Atoms which share pairs of electrons
What are the particles in metallic bonding?
Metal atoms which share delocalised electrons
Where does ionic bonding occur?
Compounds formed from metals combined with non-metals
Where does covalent bonding occur?
Most non-metallic elements (including the halides) and in compounds of non-metals
Where does metallic bonding occur?
In metallic elements and alloys.
What is an ion?
A charged particle.
What type of elements lose electrons from their outer shell to form positive ions?
Metals
What type of elements gain electrons into their outer shell to form negative ions?
Non-metals
Which group in the periodic table do ions (produced by metals in group 1 and 2 and non metals in groups 6 and 7) resemble/have the electronic structure of?
The noble gases (group 0) because they have a full outer shell.
What does the ending ‘ide’ indicate?
That a non-metal is a negative ion (anion)
What should you do when drawing a dot and cross diagram?
-Only draw the outer shells
-Don’t draw the circles
-Dots represent electrons on the metal
-Crosses represent electrons on the non-metal
How do you draw a dot and cross diagram?
-Draw the elemental symbol for each element (e.g. K + I)
-Draw dots around one and crosses around the other to show the electrons on the outer shell only
-Draw an arrow
-Draw the elemental symbols again
-Draw the new electron configuration on the outer shell of the non-metal (with dots to show which electrons have been transferred)
-Draw square brackets around each
-Write the charge of the ion on the top right hand corner outside the bracket
-Write the electron configuration (so how ALL the electrons are arranged) in normal brackets underneath EVERY elemental symbol.
Written explanation for ionic bonding
- …atom loses …electron(s) to become a … ion.
2….atom gains…electron(s) to become a…ion.
- The two ions now have a full outer shell
- They are strongly attracted to one another by electrostatic forces so form an ionic bond (as they are oppositely charged).
- …(name the compound) something ‘ide’ is formed.
What is an empirical formula?
A formula that shows the elements in a compound in their simplest whole-number ratio.
Charges on ions in a compound must…
balance
Why do compounds such as Na₂O have elements reacted in a 2:1 ratio?
The metal ion has a 1+ charge but the non-metal ion has a 2- charge. The charges must balance.
What will ionic compounds look like?
Crystals.
Are Ionic compounds soluble?
Yes, they can become an aqueous solution because ions are charged and attracted to water molecules.
What do electrostatic forces of attraction do? (in terms of bonding)
Hold ions together in an ionic lattice
Why can ionic compounds conduct electricity when molten or aqueous, but not when solid?
-When solid, ions are fixed in the lattice so cannot move.
-Ions in the molten or aqueous state are free to move and carry a charge. (charge can flow)
How can we represent ionic compounds?
-Dot and cross diagrams
-Ball and stick models
-2D diagram
-3D diagram
What is an ionic lattice?
A giant, regular structure of ions held together by electrostatic forces of attraction in all directions between the oppositely charged ions.
In which direction do electrostatic forces of attraction act?
All directions forming an regular 3D lattice structure (this is ionic bonding).
Structure of Sodium Chloride?
Each Sodium ion is touched by six chloride ions, and vice versa.
This structure repeats itself over vast numbers of ions.
This is the only ionic compound you need to know the structure of.
Ionic lattice
Millions and millions of ions packed together in a regular cubic arrangement, joined by ionic bonds.
Why do ionic compounds have high melting and boiling points?
It takes a lot of energy to overcome the strong electrostatic forces of attraction between ions.
What is a problem with representing ionic lattices using the ball and stick model?
-The model isn’t to scale, so the relative sizes of the particles may not be shown
-It looks like there are gaps between the ions.
What is a problem with representing ionic lattices using the 3D space filling model?
-The ions look like solid spheres.
-Only lets you see the outer layer of the compound
How would you use a dot and cross diagram to write the empirical formula for the compound it represents?
Count how many atoms there are of each element then use it to write the formula.
What is a covalent bond?
A shared pair of electrons between non-metal atoms
Why are some atoms more likely to form ions?
Atoms which need to gain or lose only 1-2 electrons are more likely to become ions, compared to those which need to gain or lose 3-4.
This is because gaining or losing electrons requires a lot of energy.
We add brackets round 2 elements in a compound if…
…there are 2 or more lots of them.
e.g. Ca(OH)₂ or Al₂(SO₄)₃
Hydroxide ion
OH-
Sulfate ion
SO₄²⁻
Nitrate ion
NO₃-
Carbonate ion
CO₃²⁻
Ammonium ion
NH⁴⁺
What does the molecular formula show?
The actual number of atoms of each element present in a compound or molecule.
How do you find the molecular formula of a compound, given the empirical formula, and the Mr?
- Find the Mr of the empirical formula.
- See how many times the Mr of the empirical formula goes into the unknown compound’s Mr.
- Look at the empirical formula, and multiply all the numbers by the multiple you just found.
How do you find the molecular formula of a compound, given masses (or percentages).
- Assume 100g if the compound is present. This changes the percentage given to you in the question into grams.
2.Convert these masses to moles (moles = mass/Mr)
- Divide both the mole values you calculated by the lower number of the two to get the smallest whole number ratio between the two elements (just round the other number to the nearest whole number).
Polymers
Very large molecules made when hundreds of monomers covalently bond to form long chains.
What can ions be?
-Single atoms (e.g. Cl-)
-Groups of atoms (e.g. NO₃-)
What is another way of saying ‘full outer shell’?
‘Stable electronic structure’
What does the charge on an ion represent?
The number of electrons lost or gained.
For example, a charge of 3+ represents 3 electrons lost.
What happens when a metal atom reacts with a non-metal atom?
Electrons in the outer shell of the metal atom are transferred.
Metal atoms lose electrons to become positively charged ions.
Non-metal atoms gain electrons to become negatively charged ions.
What is the technical name for positive ions?
Cations
Which elements form ions most readily?
Those in groups 1,2, 6 and 7.
What type of ion do group 1 elements form?
1+ ions
What type of ion do group 2 elements form?
2+ ions
What type of ion do group 7 elements form?
1- ions
What type of ion do group 6 elements form?
2- ions
Why do ions in the same group form ions with the same charges?
-Elements in the same group all have the same number of outer electrons.
-So, they have to lose or gain the same number to get a full outer shell.
-This means they form ions with the same charges.
What is the half equation for the ionic bonding of sodium?
Na → Na⁺ + e⁻
What is the half equation for the ionic bonding of Magnesium?
Mg → Mg²⁺ + 2e⁻
What is the half equation for the ionic bonding of Chlorine?
Cl + e⁻ → Cl⁻
What is the half equation for the ionic bonding of Oxygen?
O2 + 4e-→ 2O²⁻
What are the issues with dot and cross diagrams?
They don’t show the structure of the ionic compound, the size of the ions, or how they’re arranged
For dot and cross diagrams, where do we position the different elements?
e.g. the oxygen between the two sodium
The new electronic configuration under the old one for more complex diagrams with an arrow to show old → new
What is an ionic compound?
A giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions.
These forces act in all directions in the
lattice and this is called ionic bonding.
A single crystal of sodium chloride (table salt) is…
…one gigantic ionic lattice.
The Na⁺ and Cl⁻ ions are held together in a regular lattice.
The Na⁺ and Cl⁻ ions alternate
3D Space-filling model positives
-Shows the relative sizes of the ions
-Shows the regular pattern of an ionic crystal
Ball and stick model positives
-Shows the regular pattern of an ionic crystal
-Shows how all the ions are arranged
-Suggests that the crystal extends beyond what is shown in the diagram
What happens when ionic compounds dissolve in water?
The ions separate and are free to move in the solution, so can carry electrical charge.
Only some ionic compounds can dissolve in water.
What are the limitations of dot and cross diagrams?
-Do not show the relative size of atoms
-Don’t show how the atoms are arranged in space
-Electrons are shown differently for each atom, where in reality they are the same
Why are covalent bonds very strong?
The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces.
Limitation of 2D models to show ionic compounds.
It does not show where the ions are located on the other layers.
This is important because there could be different arrangements of ions.
How would you use a 3D diagram to write the empirical formula for the ionic compound it represents?
-Use it to work out what ions are in the ionic compound.
-Balance the charges of the ions so the overall charge on the compound is zero.
Where do atoms share electrons?
Only in their outer shells (highest energy levels).
What does each single covalent bond provide?
One shared electron for each atom.
What does each atom involved in covalent bonding generally make enough bonds to do?
Fill up its outer shell, giving them the electronic structure of a noble gas, which is very stable.
Covalently bonded substances may consist of…
…small molecules.
Some covalently bonded substances have…
-very large molecules, such as polymers
-giant covalent structures, such as diamond and silicon dioxide
How can we represent the covalent bonds in molecules and giant structures?
-Dot and cross diagrams
-Dot and cross diagrams without the orbitals
-Displayed formula (with covalent bonds as single lines between atoms)
-3D models
Limitations of displayed formulae
-Don’t show the 3D structure of the molecule
-Don’t show which atoms the electrons in a covalent bond have come from
(but useful for representing large molecules)
How do we draw dot and cross diagrams for covalent compounds?
Draw shared electrons in the overlap between the outer orbitals of two atoms.
3D model of simple molecular compounds (e.g. ammonia) positives
-Shows the atoms, the covalent bonds, and their arrangement in space next to each other
3D model of simple molecular compounds (e.g. ammonia) negatives
-Confusing when representing larger molecules (too many atoms to include!)
-Doesn’t show where the electrons in the bonds have come from
How do we work out the molecular formula of a simple molecular substance, from ANY diagram?
Count how many ATOMS of each element there are.
What does the molecular formula show you?
How many atoms of each element are in a molecule.
What does n represent when representing polymers?
a large number.
What structures do substances containing covalent bonds usually have?
Simple molecular structures.
What are substances that consist of small molecules usually?
Gases or liquids that have relatively low melting points and boiling points.
Why are the melting and boiling points of simple molecules relatively low?
The intermolecular forces between molecules are weak, so do not require much energy to overcome.
Therefore, melting and boiling points are relatively low because the molecules are easily parted from each other.
Why do larger small molecules/simple molecular substances have higher melting and boiling points?
The intermolecular forces increase with the size of the molecules, which take more energy to overcome.
Why don’t small molecules/simple molecular structures (same thing) conduct electricity?
The molecules do not have an overall electric charge because there are no free electrons or ions.
What are bulk properties?
Properties due to many atoms, ions or molecules acting together.
What are the atoms within simple molecular substances/small molecules held together by?
Strong covalent bonds.
What are molecules held together with? (small molecules)
Weak intermolecular forces.
Name the simple molecular structures you must learn.
Hydrogen, Chlorine, Oxygen, Nitrogen, Water, Methane, Hydrogen Chloride, Ammonia
H₂
Hydrogen
Cl₂
Chlorine
O₂
Oxygen
N₂
Nitrogen
H₂O
Water
HCl
Hydrogen Chloride
CH₄
Methane
NH₃
Ammonia
Why do ionic compounds have high melting and boiling points?
The ions are held together by strong electrostatic forces of attraction which require a lot of energy to overcome/break.
How are the three states of matter shown in chemical equations?
As state symbols.
What is the state symbol for an aqueous solution?
(aq)
What is the state symbol for a liquid?
(l)
What is the state symbol for an gas?
(g)
What is the state symbol for a solid?
(s)
Students should be able to include appropriate state symbols in…
…chemical equations for the reactions in the specification.
What do metals consist of?
Giant structures of atoms arranged in a regular pattern.
What are the electrons in the outer shell of metal atoms?
Delocalised
What gives metallic bonds?
The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole giant structure.
There are strong electrostatic forces of attraction between the positive metal ions and the shared negative electrons.
These electrostatic forces hold the atoms together in a regular structure and are known as metallic bonding.
What gives rise to strong metallic bonds (simple)?
The sharing of delocalised electrons
Is metallic bonding strong or weak?
Very strong
What causes all the properties of metals?
The delocalised electrons in the metallic bonds.
Why are most metals solid at room temperature?
Metals have giant structures of atoms with metallic bonding.
The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so require lots of energy to overcome/break.
This means that most compounds with metallic bonds have very high melting and boiling points.
So, they’re generally solid at room temperature.
Why are metals good conductors of electricity?
The delocalised electrons can move throughout the giant structure, carrying electrical charge and thermal energy.
(charge because the electrons are negatively charged)
Why are metals good conductors of thermal energy?
Energy is transferred by the delocalised electrons.
Why are pure metals malleable?
Atoms are arranged in layers, which allows them to slide over each other.
So, metals can be bent and shaped.
Why are metals often mixed with other metals to make alloys?
Pure metals are too soft for many uses and
so are mixed with other metals to make alloys which are harder.
Explain why alloys are harder/stronger than pure metals.
e.g. Magnesium atoms are larger than e.g. Aluminium atoms.
This means that the regular arrangement of Aluminium atoms is distorted so the layers can no longer slide over each other as easily.
How large are the molecules that make up a polymer?
Very large.
How are polymers held together?
-Strong covalent bonds between the atoms (which make the molecules)
-Weak intermolecular forces between molecules.
(However, because of the large size of polymer molecules, the intermolecular forces add up to be quite strong.)
Why are polymers solids at room temperature?
Due to the large size of polymer molecules, the intermolecular forces between them are relatively strong.
So, they take a relatively large amount of energy to overcome/break. (more than for simple covalent molecules).
What is the repeating unit of a polymer?
The shortest repeating section of a polymer.
This is the part you draw in the brackets but make sure you extend the bonds either side.
What is the molecular formula of poly(ethene)?
(C₂H₄)n
Why do polymers generally have lower boiling points than ionic or giant molecular compounds?
The intermolecular forces are weaker than chemical bonds so take less energy to overcome/break.
(hence many polymers melt easily)
What does the state of a substance at a certain temperature depend on?
How strong the forces of attraction are between the particles of the material.
What does the strength of the forces of attraction between the particles of a material depend on?
-The material (structure of substance and type of bonds holding particles together)
-The temperature
-The pressure
What can particles be?
Atoms, ions, or molecules.
What are molecules?
Groups of two or more atoms bonded together.
What processes take place at the melting point?
-Melting
-Freezing
What processes take place at the boiling point?
-Boiling
-Condensing
How can the three states of matter be represented?
By a simple model where particles are represented by small, solid, inelastic spheres.
What can the particle theory help to explain?
Melting, boiling, freezing and condensing.
What does the amount of energy that a substance needs to change state depend on?
The strength of the forces between the particles of the substance.
The stronger the forces between the particles, the higher the melting point and boiling point of the substance.
The nature of the particles involved (in a state change) depends on…
…the type of bonding and the structure of the
substance.
What are some limitations of the particle model?
-There are no forces shown
-All particles are represented as solid spheres
Do atoms themselves have the bulk
properties of materials?
No, as they depend on how many atoms interact.
What are the forces of attraction like in solids?
-In solids, there are strong forces of attraction between particles
-This hold them together in fixed positions to form regular lattice structures (arrangement)
What are the forces of attraction like in liquids?
-In liquids, there is a weak force of attraction between the particles
-So, they are randomly arranged and are free to move past each other
-However, they are still touching
What are the forces of attraction like in gases?
-In gases, the force of attraction between the particles in very weak
-So, the particles are free to move and are far apart
Particles in solids
-Particles vibrate around fixed positions
-So, all solids have a definite shape and volume, not flowing like liquids
-The hotter the solid becomes, the more the particles vibrate, causing the solid to expand slightly
Particles in liquids
-Particles are constantly moving with random motion
-The hotter the liquid gets, the faster they move, so the liquid expands slightly when heated
Do liquids have a definite volume?
Yes, but they don’t have a definite shape, and will flow to fill the bottom of a container
Do gases have a definite volume?
NO, they don’t have a fixed volume or shape and will always fill any container.
Particles in a gas
-Particles are constantly moving with random motion
-The hotter the gas gets, the faster they move, so the gas either expands when heated or their pressure increases
-The particles in a gas travel in straight lines
What state is a substance in if the temperature is below the melting point?
Solid
What state is a substance in if the temperature’s above the boiling point?
Gas
What state is a substance if the temperature is between the melting and boiling point?
Liquid
What do changes of state change?
Because they are physical changes, changes of state don’t change the particles themselves, just their arrangement or their energy.
What are substances that consist of giant covalent structures?
Solids with very high melting points.
ALL of the atoms in these structures are
linked to other atoms by strong covalent bonds.
These bonds must be overcome to melt or boil these substances.
Give examples of giant covalent structures.
-Diamond (form of carbon)
-Graphite (form of carbon)
-Silicon dioxide (silica)
Giant covalent structures are…
Macromolecules (very large molecules made of many small units called monomers).
Do giant covalent structures conduct electricity?
No, not even when molten (bar weird ones like graphite).
This is because they don’t contain charged particles.
Predict, with reasoning, whether diamond or poly(ethene) has a higher melting point (3)
To melt diamond you have to break the covalent bonds between atoms which are very strong, but to melt poly(ethene) you only have to break the weaker intermolecular forces which takes less energy.
So, diamond has the higher melting point.
Silicon dioxide
-Sometimes called silica
-This is what sand is made of
-Each grain of sand is one giant structure of silicon and oxygen
How can we deduce the number of atoms from a chemical formula e.g. Na₃AlF₆
Count the number of times each element comes up, so in this case:
Na = 3
Al=1
F=6
3+1+6=10 atoms.
What are polymers?
Large, chain-like molecules that can extend for thousands of atoms.
Why are covalent bonds strong?
Because the shared electrons are attracted to the nucleus of both atoms.
Give examples of a small covalent molecules
Water
Oxygen
Carbon dioxide
Give an example of a giant covalent structure
Diamond
Graphite
Give an example of a polymer
Poly(ethene)
Poly(propene)
Give examples of large covalent molecules
Polyester
Long chain alkanes
Sucrose
Which is harder: graphite or graphene?
Graphene
