Atoms, elements and compounds part two.

what are properties of compounds?

the properties are usually completely different from the elements that the compound is made from

compound vs mixture vs element

element:

susbtance made of only type of atom.

each element has its unique properties

cannot be broken into simpler substances

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compounds:

made of two or more different type of atoms chemically combined together

compounds have their own unique properties that are different to the elements that make them up

compounds cannot be separated physically. they can only be separated into elements chemically.

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mixture:

material that contains 2 or more elements or compounds not chemically bonded to together

the components in a mixture keep their individual properties

can be separated physically

properties of simple molecular compounds?

low melting and boiling points, often gases at room temp - They are made of simple covalent molecules.

The intermolecular forces/attractive forces between molecules are very weak.

Not much energy is required to overcome and break these forces.

do not conduct electricity - they have no free electrons or ions present to carry the electrical charge

ionic bond

strong electrostatic attraction between oppositely charged ions

properties of ionic compounds

they have high melting and boiling points - ions r attracted to each other by strong electrostatic forces. large amounts of energy r needed to separate them.

they conduct electricity when molten or dissolved in water (when not solid) - when molten or dissolved the ions r free to move and carry charge

soluble in water - do not need to explain why

what is the electrical value of any ionic compound

electrically neutral

diamond properties

appearance: colourless. transparent crystals that sparkle in light. use: jewellery

hardness: hardest natural substance. use: cutting tools. Why: Giant covalent structure. Each carbon atom is covalently bonded to four others. The covalent bonds between the carbon atoms are very strong.

conductivity: does not conduct electricity

diamond bonding

does not conduct electricity - all of the outer electrons are used to form covalent bonds. there are no electrons free to move, so none to carry charge.

high melting and boiling point - each carbon atom is covalently bonded to four others. the covalent bonds holding together the carbon atoms r strong and hard to break.

graphite properties and uses

appearance: dark grey, shiny solid

soft - the layers can slide over eachother - used as a lubricant and in pencils

conducts electricity and inert - so used as electrodes

high melting and boiling point

Structure of graphite: Layers. Hexagonal rings of carbon.

graphite bonding

giant covalent.

(opposite is simple covalent like CO2) each carbon atom is covalently bonded to 3 other carbon atoms

graphite has free/delocalized electrons. these electrons can move through the structure and carry charge.

strong covalent bonds between carbon atoms - hard to break/overcome these bonds so high melting and boiling point

silicon(IV) oxide, SiO2 and diamond similarities

* both have a rigid tetrahedral arrangement of atoms
* all the atoms in these structures are held together by strong covalent bonds
* both SiO2 and diamond have high melting and boiling points
* both r hard
* both don’t conduct electricity as there r no electrons free to move through the structure and carry charge

why can layers of graphene slide over each other

between the layers there r weaker forces of attraction, so the layers r able to slide or slip over eachother

metal properties

high melting and boiling points - large amounts of energy r needed to overcome the strong forces of attraction between the positive metal ions and sea of delocalised electrons

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conduct electricity - metals have delocalised electrons which can move through the structure and carry charge

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metals malleable and ductile - the positive ions r arranged in layers. when a force is applied the layers can slide over each other.

metallic bonding

the electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons

metal structure

Regular arrangement or lattice of positive ions.

giant lattice structure of ionic compounds

a regular arrangement of alternating positive and negative ions

silicon (IV) oxide structure

• tetrahedral structure

• each Si atom is covalently bonded to four oxygen atoms.

• each O atom is CB to two silicon atoms