Metals Flashcards
Physical properties of metals
Lustrous: How well the substance reflects light. Most metals can be polished to a high lustre ie shiny, reflective.
Malleability: can be beaten/pressed into various shapes without breaking.
Electrical conductivity: are good conductors because electrons are delocalised therefore free to move and carry charge
Ductility: can be drawn into wires
State at room temperature: solid except mercury because of high melting and boiling points.
Melting point: Pure metals have a precise melting point. Varies from 100°C - above 1000°C
Boiling point: Pure metals have a precise boiling point. Most metals have boiling points above 1000°C.
Thermal conductivity: how easily heat energy can be passed through a substance. Metals are good conductors of heat as atoms are tightly packed together.
Sonorous: ring when struck
Density: gmL-1 Most metals have high densities (above 3gmL-1) except Na and Li which can float on water (ie less than 1gmL-1)
Colour: related to a substance’s ability to reflect light. Most metals are silver-grey. Copper is pink and gold is yellow.
Hardness: many pure metals such as Mg, Al or Fe, are too soft to be used for engineering purposes and are hardened by making an alloy of the metal. Lithium and Na are soft enough to be cut by a knife
Lustre of metals
All metals have a high lustre. However, some metals have a dull appearance due to their reaction with oxygen or water in the atmosphere.
Colours of metals
Silver grey: Ca, Fe, Pb, Li
Silver: Al, Mg, Ag, Na, Zn
Pink: Cu
Gold: Ag
Density of metals
Metals have high densities because the atoms are tightly packed together. When a layer of atoms is placed on top of another layer, the atoms move into the gaps between the atoms of the previous layer.
A metal’s density depends on their atomic masses and how tightly packed the atoms are.
An atom in the middle of arrangement touches 6 other atoms.
Electrical conductivity of metals
Metals are good conductors of electricity because the valence electrons are delocalised and therefore free to move within the metal structure. So when electrons flow out of the negative terminal of a power supply and into a metal, the electrons within the metal are able to carry the current to the positive terminal of the power supply.
Why do metals have high boiling and melting points
Because there are strong forces of attraction between the atoms due to the delocalised valence electrons. Because the e- are free moving, a metal actually consists of positive ions (the nuclei) surrounded by a sea of e-. The sea of e- are attracted to the neighbouring positive ions, meaning that these attractive forces require a lot of energy to break.
Delocalised - can be attracted to other positive nuclei.
Malleability and Ductility
The attractive forces between atoms is strong, however, they are not rigid (fixed in place). Layers of atoms can slide over each other when a force is applied. When the force is removed the atom’s closely packed arrangement is restored. The atoms slide and settle into a new position once the force is removed.
Metallic bonds are non-directional.
Thermal conductivity
Particles inside a metal vibrate in a fixed position. The particles closest to the heat source gain Ek and vibrate more vigorously. These more energetic particles collide with the unheated particles, passing some of the Ek on and also causing those particles to start vibrating more vigorously. The process of particles colliding continues. Heat energy is transferred from the hot end of the rod, to the cold end, until the entire thing is hot.
What is an alloy
A mixture of two or more elements in a solid solution in which the major component is a metal
How are alloys made
By mixing two or more molten metals (components) and allowing the mixture to cool. This makes a mixture, NOT compound, meaning that they have variable composition and properties depending on how much of each metal/non-metal is added.
Eg of alloys
Bronze: Copper and tin. Protects itself with an attractive coating that lasts for centuries.
Brass: Copper and zinc. Does not corrode as easily as Cu and retains an attractive lustre. Retains good electrical conductivity of Cu.
Steel: Iron and carbon.
Solder: Tin and lead - melts at a lower temperature than either Sn or Pb and can bond with many metals.
Duralumin: Aluminium, Cu and Mg - has greater strength than Al but retains the low density needed for aeroplane construction.
Where are alloys used
Where they have properties that are different to the metals they contain, so they become more useful than the separate component metals
Do alloys have specific melting points
No because it is a mixture of metals
Describe steel
Fe and C (0.5-2%)
It’s harder, stronger and more flexible than iron and doesn’t corrode as quickly as iron.
High tensile strength - can be bent and return to their original shape without breaking.
Why are alloys harder than pure metals
Because adding different sized atoms breaks up the regular arrangement (crystalline structure lattice) of atoms in a metal. This means when a force is applied to an alloy the atoms cannot slide pass each other as easily as they can in a pure sample of the metal.
The atoms of the different size replaces a small number of atoms of the parent metal. The layers of atoms cannot move over each other as well (up to a point), making the alloy harder than pure metal. Less force is required to make the atoms slide past each other in pure metals.
Atomic structure of metals
Atoms are strongly attracted to each other so they form a close-packed lattice, which results in a hard crystalline material.
Once the percentage of the larger atom increases, what happens
There is more space between the metal atoms, so the atoms are able to slide past each other more easily. It begins to approach the relative strength of the element. Disrupts the regular arrangement of the smaller atoms to the point that the smaller atoms cannot bond together as strongly.
Reaction of metals and acid
Metal + Acid -> Metal salt + hydrogen
Test for hydrogen with lit splint
What is the common feature of metals
Low number of valence electrons.
