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Chapter 2 – Elements, compounds and mixtures
Key points Checklist Everything in the known universe is made up of the elements found on the periodic table. There are over 100 different elements, which are made up of atoms. Particle diagrams are used to help explain elements, compounds and mixtures. Some elements exist as individual atoms, but some bond together to form molecules of atoms of the same element. Everything in the known universe is made up of the elements found on the periodic table. There are over 100 different elements, which are made up of atoms. Matter 死死 – substance 死死 Solid (room temp) Liquid (room temp) Gas (room temp) Macro 死死 view Iron bar Fe Salt NaCl Chlorine Cl 2 Water H 2 O Oxygen O 2 Carbon dioxide CO 2 Element Compound Element Compound Element Compound Micro 死死 view Particle model
- all are viewed as particle Sub-atomic model -atom, ion (charged atom) Molecule (same type of atoms or different type of atoms) Atom Single atom exist alone Ion (charged atom) Different atoms form a building block Molecule of same type 2 same atoms must exist in pair Note S 8 molecule of different type Different atoms form a building block Molecule of same type 2 same atoms must exist in pair molecule of different type Different atoms form a building Block
Element - same atoms Compound - different atoms Element 死死 Compound 死死死 Element Compound Element Compound
Elements
An element 死死 is a pure substance that cannot be broken down into any other substances. An element is made from just one type of atom, and examples include oxygen, hydrogen and iron. Some elements exist as individual 死死 atoms (solid: iron Fe), but some exist as molecules.(liquid: chlorine Cl 2 , gas: oxygen O 2 , hydrogen H 2 ) Did you know? Most of the elements are metals. Aluminium (Al) is used to make bike frames 死 死 死 because it is light. It is also used to make kitchen foil. Copper (Cu) is used to make electrical wires because it is a very good conductor of electricity. (90% are compound, plastic, clothes etc) How many chemical elements do you think there are? The ancient Greeks thought that there were just four elements - earth, air, fire and water. However, we now know that there are actually 118 chemical elements. Everything on Earth and in the solar system is made from these elements. A few of these elements can be found pure in a natural state 死死死死. For example, graphite and diamond can be found in rocks in the Earth’s crust, and they are forms of the element carbon(C). Gold is an example of a metal element that can also be found in rocks. The air we breathe is mostly made from nitrogen N 2 and oxygen O 2 , both of which are elements. All the atoms in a copper wire are the same. These are different to the atoms in aluminium foil which are all the same as each other. 死死 The periodic table There are 118 chemical elements. They are listed on the periodic table in a specific order.
Atom a solid
- A solid element The particles are close together and arranged in a regular way. liquid
- A liquid element The particles are close together and arranged in a random way. gas
- A gaseous element The particles are far apart and arranged in a random way. Molecules Some non-metal elements are made from atoms which are bonded into clusters called molecules. For example, oxygen is a gaseous element made from molecules. A molecule is made up of 2 or more atoms. These can be the same type or different.死 死死死
Compounds 化化化 (within building block)
A compound is a pure substance that is made from more than one element(only one type of particle). In a compound, elements are chemically bonded together, which makes it very difficult to separate them. 死死 When a compound is made, the atoms of the elements bond together in a fixed ratio. This means that each compound can be represented by a chemical formula. For example, the formula of water is H₂O (2:1) and the formula of carbon dioxide is CO₂. (1:2) To break apart the elements in a compound, a chemical reaction must take place, for example, electrolysis or thermal decomposition. However, when elements make a compound through a physical process such as filtration or boiling, it is impossible to separate them. 死死 Compounds are not found on the periodic table. 死死 For example, water isn’t on the periodic table because it is a compound, not an element. Water is made from the element hydrogen bonded to the element oxygen. Particle diagrams - compounds A particle diagram for a compound will show more than one type of atom.
Compound of Solid Block:NaCl Compounds including both a metal element and a non-metal element bonded together do not form molecules. 死死. They form ionic compound. If this 3D particle diagram for sodium chloride was shown on a large scale, it would show the same number of metal sodium atoms (grey) as chlorine atoms (green), because the formula is NaCl Compound of liquid Block:H 2 0 Water molecules are made up of two elements or 2 different atoms - hydrogen (blue atoms) and oxygen (red atoms). Water has a specific ratio of two hydrogen atoms to one oxygen atom. (2:1 ratio) Compound of gas Block:CO 2 Carbon dioxide molecules are made up of two elements or 2 different atoms - carbon (black atoms) and oxygen (red atoms). Carbon dioxide has a specific ratio is one carbon atom to two oxygen atoms. (1: ratio)
Mixtures 化化化 (between building blocks)
A mixture is formed when two or more elements or compounds are present without being chemically bonded together. The substances which have been mixed are not present in specific amounts or ratios like they are in a compound, e.g. two hydrogen atoms for each oxygen atom in water. They can be in any combination, e.g. for a mixture of sand and water you could have any amount of sand with any amount of water. In a mixture, the two ingredients can be separated using physical processes, 死死 without chemical reactions. This is because they are not chemically bonded together. Here are some examples: A mixture of sand SiO 2 (compound) and water H 2 O (compound) can be separated using filtration.
Pure substance 死死死 Mixture 死死死 solid Gas Solid + Solid Solid + liquid Liquid + liquid Liquid + gas All gases Cu O 2 Fe +S 8 NaCl+H 2 O Cl 2 +H 2 O H 2 +H 2 O Air = N 2 +O 2 +CO 2 copper Oxygen Iron + sulfur salt + water chlorine+ water hydrogen
water nitrogen+ oxygen+ carbon dioxide element element element
element compound
compound element + compound element
compoun d element + element + compound magnet distillation Liquid element: silver Hg 死死 114 422
