Chemistry Test 3 Flashcards
List the properties of a metal
- High melting and boiling points
- Good conductors of electricity and heat
- Malleable; shaped by beating or rolling
- Ductile; drawn to wire
- High Density; hard with a high tensile strength
- Lustrous; shiny or reflective
- Reactive (corrosive)
- Have low ionisation energies (measure of the energy required to remove an electron of a gaseous atom)
- low electronegativity ( a measure of the tendency of an atom to attract a bonding pair of electrons
- react by losing electrons
Explain why metals have a high boiling and melting points
Strong electrostatic forces takes a lot of energy the to break apart the attractive forces in a metal
Why are metals good conductors of heat and electricity in solid and molten state.
The sea of charges and delocalised electrons which carry the electric current or heat energy to pass and cross through quickly lattice
Why are metals ductile and malleable?
The non-directional bonding in the metal means atoms can move out of the way when being manipulated
Why do metals have a high density?
The atoms are closely packed and clustered tightly together in the lattice structure
Why are metals lustrous?
The free electrons within the metal reflect light
Why are metals reactive?
The free electrons within the metal can be easily removed from the atom.
What are the main differences between the properties of the main group and transition group metals?
- Transition metals are harder
- Transition metals are more dense
- Transition metals have higher melting points
- transition metals have strong magnetic properties
- transition metal compounds tend to be brightly coloured
What is an ionic compound?
Ionic compounds are made by the combination of atoms or groups of atoms, where electron/s are transferred from one another.
They form a crystal lattice made up of positive and negative ions
What is ionic bonding?
Ionic bonding is a chemical bonding between a metal and a non metal, that involved the transfer of electrons from 2 or more atoms.
Why do ions form?
Ions are former when atoms lose or gain electrons in order to fulfil the octet rule and have full outer valence electron shells.
What type of force is responsible for holding the actions and anions together in an ionic lattice?
Electrostatic attraction / force exiting between the positively and negatively charged atoms
Explain the formula for Sodium chloride
In the case of sodium chloride, in order to maximise the forces of attraction, each sodium ion (Na+) is surrounded by six chloride ions (Cl-) and each chloride ions is surrounded by six sodium atoms.
1:1 ratio that is why it is written NaCL
List the properties of ionic compounds
- high melting and boiling points ( Solids at room temperature)
- Hard but brittle
- Do not conduct electricity in solid state
- good conductors of electricity in liquid or dissolved state
- vary from being soluble and insoluble in water
- not malleable or ductile
Explain why ionic compounds have melting points
Ionic bonds are very strong (due to electrostatic forces between the + and - ions), so a large amount of energy is required to break the bonds,
Strong electrostatic forces hold the + and - ions in fixed positions therefore High amount of energy is needed to disturb bonds.
Eg.
- Magnesium oxide is used to line furnaces
- Ceramic materials contain a mixture of strong ionic and covalent bonds which help be a part of engine parts
Explain why ionic compounds are hard but brittle
- Solid ionic compounds feel hard but can be easily broken when force is applied
- It feels hard because the electrostatic force hold the ions close together making it feel tough.
- When force is applied the ions are disturbed and moved from the fixed positions in the lattice (+-+-+-) to like charges (++++) causing repulsion, thus they break apart.
Eg.
- Calcium phosphate makes up Bone tissue (strengths bone but can break)
- Granite, limestone and Sandstone ( why they easily crumble but are heavy)
Why are ionic compounds good conductors of electricity in a liquid state?
In an aqueous solution (polar solvents such as water) the compounds dissolves and disassociates. This means there are free particles which are able to direct and move the current along.
However this cannot occur in a solid lattice because the particles are fixed in organised locations.
Eg.
- Ammonium Chloride is used as electrolyte in dry batteries which in solution allow current to flow in battery
- Potassium hydroxide is used as an electrolyte in ‘push’ remote buttons
Why are ionic compounds soluble in polar solvents.
Ionic compunds daily disobe in solvents becaus the positive particles move and dissociate from the compound.
Eg when the slightly negative oxygen in water molecule surrounds the +tive particle and pulls into solution.
Same for -tive particle but with H+
Eg, Coffee, Salt Water
What is Metallic Bonding
Metallic bonding is the electrostatic forces of attraction between actions and the electrons that are free to move within the regular lattice structure metal.
In a metallic bonding model, positive metal cations are surrounded by a sea of delocalised electrons
What are delocalised electrons?
Negatively charges electrons which are able to move freely throughout the lattice and belong to the lattice as a whole, rather than in a shell of one atom
What is the metallic bonding model?
A structure developed by chemists as model for the structure of metals called the metallic bonding model
How can a metal be modified?
Through alloy production
Heat treatment
Formation of nano sized structures
How to make an alloy?
Metals are mixed with small amounts of another substance, usually a metal or carbon.
The substances are melted together, mixed and then allowed to cool.
The resultant solid is an alloy
Varying compositions of alloys can obtain materials with specific properties.
How are properties in alloys different to pure metals?
When other metals or carbon are added to melted metals, the substance that is produced is called an alloy.
Alloys tend to have improved properties compared to the original metal, making them more useful.
Alloy is harder and melts at a lower temperature than the pure metal.
- this is because atoms of different sizes are now included in the metal lattice. These atoms do not pack in the same way as the main metal p, they will not allow the lattice to shift and bend the same way. The disruption of the regular metallic lattice also accounts for the lowered melting point.
Explain Carbon Steel
Interstitial alloy where a small proportion of an element with significantly smaller atoms are added to the metal.
The added atoms sit in interstices (very small spaces) between metal actions in a metallic lattice
- Carbon is harder and less malleable than pure iron. Varying amount of carbon in the mixture produced steels with different properties, allowing steel with the most suitable properties to be used in specific applications.
Summary of the properties and uses of some different carbon steels
Low carbon steel (less than 0.3%) - strong, easily shaped - for bridges, buildings, ships and vehicles
Medium carbon steel (0.3-0.45%) - increased hardness, tensile strength, decrease ductility - large machinery
High carbon steel (0.45-0.75%) - very strong, more brittle - springs, high-strength wire
Very high carbon steel (up to 2.5%) - hard, more brittle - cutting tools
Elements alloyed with iron to make steel which are substitutional alloys
Atoms are too big to fit in the metallic lattice. The atoms of the element sometimes replace some of the iron and the mixture is called substitutions alloy.
Metallic elements added to make substitutional alloys have similar chemical properties and forms cations of a similar size in the main metal
All the metal cations are attracted to the sea of delocalised electrons, so the lattice is still strong and bonded.
However, because the different kinds of atoms are slightly different in size the layers within the lattice cannot move easily past each other. Making the alloy harder and less malleable than pure iron.
Manganese- increases strength and toughness - bicycle frames
Chromium- increases hardness and tensile strength and toughness, resists corrosion - stainless steel cutlery, sinks
Nickel - increases toughness, tensile strength and hardness, resists corrosion - stainless steel
Cobalt - Imogen magnetic properties, resists high temps - Alnico magnets, jet propulsion engines
Define molecule
A molecule is a particle made up of two or more atoms that are chemically bonded together
What is a covalent molecular substance?
Covalent molecular substances are individual molecules that from covalent bonds by the sharing of electrons between non-metals
There are composed of discrete (stand alone) molecules and are soft, have low melting points and are gases and liquids in room temperature
What is a covalent network substance
It is a 3D network of an element such as carbon
They are hard very high melting points and are solids
What is covalent bonding
Is a bonding which occurs between non metals where electrons are shared to fulfil the octet rule of the valency shell.
Covalent bonds are most likely to occur when atoms have similar electronegativity because both atoms have the same affinity for electrons and neither has a tendency to donate them, they share electrons in order to achieve octet configuration and become more stable
Properties of covalent bonding
- Low Melting and Boiling Points; due to the weak intermolecular forces holding them together as a solid. This means it is easy to disturb the bond
- Non conductors of electricity; the electrons are immobile because it’s either being shared or in a position within the atom structure. So there is nothing to carry the current
- solids are usually soft and have a low because the intermolecular forces holding the discrete molecules together do not pack them tightly in a lattice, instead the attraction is very weak making the solid feel soft.
When sugar us gently heated it turns to a clear liquid. If the liquid is strongly heated it turns black and a gas is produced. Explain.
When sugar turns into a liquid, it is melting; the intermolecular forces between sugar molecules are broken.
When the liquid turns black and gas is produced, the bonds between atoms in sugar molecules are broken, allowing a new substance to form.
Define what an allotrope is
Allotropes are different structural bonds of carbon. Arranged in pentagons and hexagons. Each carbon is held together to one another by weak intermolecular forces
They form things like diamonds, graphite but are different in appearance and properties due to differing structural composition
They are covalent networks which are very hard solids with very high melting and boiling points
Difference between covalent molecular substances and networks
Substances can exit on their own without another molecule when intermolecular attraction is disturbed such as H2O
But in networks if a carbon is removed from the whole network structure, that carbon can no longer appear and be known as a diamond or graphite,instead it will be known as a carbon atom, because it is the structure which determines the appearance of the network.
Ammonium
NH4+
Cyanide
CN-
Dihydrogenphosphate
H2PO4
Ethanoate or acetate
CH3COO-
Hydrogencarbonate
HCO3-
Nitrate
NO3-
Nitrite
NO2-
Permanganate
MnO4-
Dichromate
Cr2O7^-2
