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Chemistry Summer HW, image - Coggle Diagram
Chemistry Summer HW
States of matter and mixtures
The three states of matter are: solid, liquids and gasses.
Particles in a solid are packed together and they vibrate around a fixed point. Their shape and volume are both fixed.
In a liquid, the forces of attraction are weaker between particles so their shape is not fixed and can change to fit a container its put inside.
In a gas, the particles are not held together by any force so they move in random directions very quickly.
Solid to liquid: melting
Liquid to solid: freezing
Liquid to gas: boiling
Gas to liquid: condensing
All of these are physical/state changes as they involve the forces between particles but not the particles themselves. Chemical changes are when a new product has been formed entirely.
A mixture: Consists of 2 or more elements or compounds not chemically joined together.
A pure substance: A single element or compound, not mixed with any other substance.
Different separation techniques
Simple distillation: Used to separate a pure liquid from a mixture of liquids. Works when liquids have different boiling points. Commonly used to separate ethanol from water. Ethanol has a lower bp than water so it evaporates first, the vapor is then condensed inside a condenser to form a liquid.
Fractional distillation: Oil is heated in the fractional distillation column and the oil evaporates and cools at different temperatures. Hydrocarbons in crude oil can be separated into fractions. Crude oil is continuously piped in at the bottom. The vaporised oil rises up the columns and the various fractions are constantly tapped off at different levels where they are condensed.
Filtration: If you have an insoluble substance, you can filter it by using something such as filter paper to separate the solution precipitate.
Crystallisation: If you have a soluble salt and want to separate it from a solution it was dissolved in, you need to first warm the solution in an open container, allowing the solvent to evaporate leaving a saturated solution. Then, you need to allow the solution to cool. The solid will come out of the solution and crystals will start to grow, these can be collected and dried.
Paper chromatography: Used to separate mixtures to help identify substances. Involves a stationary and mobile phase. Different compounds have different Rf values which can be used to identify what the substance is.
Key concepts in Chemistry
Ionic bonding: An ionic bond forms between a metal and non-metal. Metals ions are positively charged and non-metal ions are negatively charged which attracts them. The structure they form is an ionic lattice.
Covalent bonding: Occurs in most non-metallic elements. It is when atoms share pairs of electrons. These bonds between atoms are very strong. Simple molecular substances and giant covalent structures are two different formations they can assume.
Atomic structure
The atom is made up of a positively charged nucleus that makes up the atom's mass. It contains two subatomic particles known as protons and neutrons. Protons are positively charged whereas neutrons have no charge (neutral). Electrons are negatively charged subatomic particles and they orbit the nucleus in shells. Depending on the number of electrons in an atom's outershell and how many shells it has, we can determine how reactive it will be.
These two topics link together.
Periodic table
The periodic table is a large display that people use to show every element that has been discovered by humans so far and what they are like. The periodic table consists of information like the number of protons an element has and its mass number. The modern periodic table is arranged by increasing atomic number and elements are arranged in periods (of increasing atomic number) and groups where they have similar properties.
The period number of an element is decided by the number of electron shells it has and the group number is decided by the number of electrons in its outermost (valence) shell.
Dimitri Mendeleev created the first version of the periodic table and he ordered his table in order of atomic mass (but not always). He left gaps for elements that had not been discovered yet and he put elements of similar properties in groups.
Groups in the periodic table
Group 1 - The Alkali Metals: Physically, the group 1 elements are all soft, have low melting points and have low densities. Their chemical properties however is that they all have 1 electron in their outermost shell. This makes them very reactive as the one electron is very easy to lose. Reactivity increases as you go down the group.
Group 7 - The Halogens: The halogens all have low melting and boiling points and they increase as you go down the group. They all have 7 electrons in their outermost shell so they have similar chemical properties such as reactivity.
Group 0 - The Noble Gases: All of these elements are gases at room temperature and have low boiling points. The boiling points increase as you go down the group and they all exist as a single atom. They all have full outershells so they are extremely unreactive or inert. The density of the noble gases increases as you go down the group.
