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Chemistry Section 1 (A (States of matter (Solids (Particles close together…
Chemistry Section 1
A
States of matter
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Change of state
Solid and liquid
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Freezing
particles move less, less energy
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sublimation
a few substances have the ability to go from gas to solid with no liquid state, eg CO2
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C
Atomic Structure
elements
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Atoms
proton and neutron nucleus, electron shells
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electron
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electron arrangement
electrons occupy a particular energy level, electrons at lowest energy level in innermost shells
electrons in the same group have the same number of electrons in the highest energy level (outer shell)
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3rd shell: appears full at 8, but can expand to 18
Ions
when atoms form chemical bonds they transfer electrons to complete their outer shell. They form ions.
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Isotopes
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They have different physical properties, such as radioactivity ( C-14 and H-3), but share the same chemical properties
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F
Ionic Compounds
formation of Ions
Electrons are transferred from one atom to another (this is in an effort to either fill or empty the outer shell to become stable.)
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But an ion will have a charge: an electron has a charge of -1, so loosing an electron looses one negative charge, making the ion +1.
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Dot and Cross Diagrams
Dot and cross diagrams represent electron transfer. One atom will have dots as electrons, the other crosses.
Ionic Bonding
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they are attracted to each other due to their opposite charges, so we say the ions have electrostatic attraction.
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Breaking Ionic Bonds
To melt or boil anything, heat is used to break bonds.
The stronger the bonds, the more heat needed.
Ionic compounds have strong bonds, so they don't melt or boil unless there is a considerable amount of heat, this means the have high melting and boiling points.
The bigger the difference in charge, the stronger the attraction
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The stronger the attraction, the harder it is to break the bonds, this means that the melting and boiling points will be higher.
Ionic Crystal
An ionic crystal is a lattice of electrons in a 3D structure, the ions are alternate positive and negative and their opposing charges hold the structure together.
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Covalant Substances
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Electrons, being shared by atoms in a covalent bond, are attracted to the nucleus of each atom in the bond. Remember that electrons are negative and protons- in the nucleus- are positive.
Dot and Cross diagram
To draw a dot and cross diagram for a covalent bond, you need to draw the outer shells of the two atoms involved with an overlap, in this overlap should be the electrons they share.
Half the electrons in the overlap should be dots and half crosses, because one electron in every pair comes from each atom.
The rest of the electrons for the outer shell should be drawn on, one atom with dots, the other with crosses.
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Carbon
Graphite
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In Graphite the atoms from layers, these layers can slide over each other, this makes it very slippery and so can be used as a lubricant.
Diamond
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Diamond is extremely hard because it has a many bonds in it, this means it is great for cutting as it can cut anything.
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Metallic Crystals
In a metal atoms come together into a lattice, the electrons become detached from their atoms- delocalised- making the atoms positive ions.
Conductivity
Metals have delocalised electrons, electrons carry electricity; so because there are free electrons charge can pass easily through a metal.
maleability
The structure of a metal is with rows of atoms on top of one another, in pure metals as all the atoms will be the same size, the layers can slide easily over one another making them easy to bend.
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Electrolysis
Current
An electric current is a flow of electrons, although it can also be a flow of ions (as they have a charge.)
Covalent Compounds
In covalent compounds there are no electrons free to move, this means there can be no transfer of electricity through a covalent compound
Ionic Compounds
When ionic compounds are molten or in solution, the positive and negative ions separate this means that there are ions free to flow, and so they can conduct electricity.
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Creating Subsytances
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Positively charged ions move to one end, negatively to the other, these are then turned into atoms (by losing their charge) and so new substances are formed.
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