Yr 10 Chem
Atomic structure & the periodic table
Chemical Bonding
Chemical Reactions
Trends in chemical activity of metals
The Bohr Model and light emmision
Family groups
Valence electrons and there importance
Defenitions
The atom
Surrounding the nucleus are the electron clouds in which electrons spin around. Electrons are negatively charged
All atoms are electrically neutral.
The nucleus is at the center of the atom and has a positive charge. Almost all of an atoms mass is in the nucleus.
Mass number - the total number of particles in the nucleus (protons +neutrons)
Isotope - atoms that belong to the same element with the same number of protons and the same atomic number but a different number of neutrons giving them different mass numbers
Atomic number - the number of protons in the nucleus of an atom
Group 1: Alkali Metals - Form ions with a charge of +1. Have typical metallic properties, and display similar extreme chemical behaviour. Elements are far too reactive to be found naturally and are instead found as compounds. React violently with water.
Group 2: Alkaline Earth Metals - act similar to the group 1 elements. When they react they lose two electrons from each atom to form ions with a charge of +2
Group 18: Noble/inert gases - all elements in this group are gases and do not react with substance or are extremely reluctant to do so
Metals have a weak hold on their electrons and this weakens even further as the atoms get larger and the outer electrons are further from the nucleus they spin from
The increase in size down the groups causes metals to become less stable and more likely to react with other substances
Different elements release different amounts of energy therefore emitting different colored light
When an electron on the valence or outer shell of an electron i exposed to heat or light it will gain energy and jump from one shell to another. When an electron does this it is considered to be excited. As the electron jumps back down it emits light
Elements have different numbers of protons in their nuclei, this means that outer-shell electrons are held more tightly in some elements than others. As a result, the energy levels between and the jumps between them are different too.
Reactivity - as you go further down a group the more electrons there are meaning more shells as you get further away from the nuclei the "pull" becomes weaker meaning it is more likely to react
Properties - elements with the same number of valence electrons share many of the same properties (family grouping)
Bonding - sharing and giving valence shell electrons to other atoms
Metallic bonding
Characteristics
Bonding types
Covalent - between non-metals
Metallic - between metals
Ionic - between metals and non-metals/ions
Ionic Compounds - only soluble in polar liquids, hard but brittle, high boiling/melting points
Covalent molecular - structures consist of molecules on their own. They have low melting and boiling points. The covalent bonds between the atoms within the molecules are strong
Metals - not soluble at all, hard and strong, high melting/boiling points, conduct electricity as liquids and solids
Covalent network - made from a network of repeating lattices of covalently bonded atoms. They often have high melting and boiling points and are insoluble in water.
Metallic bonding involves metal atoms giving up valence electrons and share them with all the other atoms in the metal (delocalised electrons) they all become positive atoms
There is now a strong force of attraction from the positive ions and the negative electrons, these forces of attraction hold everything together. This gives the overall metal strength and means that most metallic structures have high melting and boiling points
In metals, the atoms are bonded toegther by a 'sea' of electrons, in most metals the atoms are packed closely together
Metals are also good conductors of heat and electricity because the delocalized electrons can carry electrical current and thermal energy through the whole structure
Metals are also malleable this is due to its regular structure, which means it has layers and these layers can slide over one another because they are not fixed.
Ionic compounds
Melting and boiling points are determined by the bonds holding the substance together and since there are a lot of bonds in an ionic compound the bond is really strong, this means more energy will be required to break those bonds and that energy is a high temperature
Covalent molecular substances (CMS) (simple molecular)
To conduct electricity you need charged particles that can move these could be ions or electrons, when ionic compounds are in there solid form everything is fixed and they can not conduct electricity, but when they are melted or dissolved in water, the ions of the compound are free to move about, and this movement of charged particles allows them to conduct electricity
Generally ionic compounds include tons of atoms not just a couple and the positive and negative ions altnerate so that each ion is attracted to each of those around it and if this happens in all directions it will form a 3D lattice
CMS do not conduct electricity because there are no free electrons and the molecules themselves do not have any electrical charge
Due to its lack off bonds in between molecules and lack of atoms in a CMS they are soft
Covalent bonds are strong and therefore would require a lot of energy to break the bonds apart, but when you melt or boil a CMS you do not break the bonds, you only need to break the bonds that exist between other molecules (inter-molecular forces), because of this you only need very low temperatures to melt or boil CMS, the more inter-molecular force a molecule has the stronger the attraction therefore requiring more energy to break
Covalent network substances (CNS) (giant covalent structure)
CNS are very strong and have high melting points this is due to the fact that they are made up of many bonds, you would need a lot of energy/heat to break apart the bonds between them
CNS do not conduct electricity due to the fact that they have no charged particles (in exception to graphite)
CNS are made of huge numbers of non metal atoms that are all bonded to each other by covalent bonds and are usually arranged in regular repeating lattices
Combination
Decomposition
Law of Conservation
The law of conservation sates that during a chemical reaction, atoms can not be created or destroyed
Combination reactions occur when reactants combine to form a single product
x + y = xy
When reactants break apart to form several products
xy = x + y
Precipitation
Some substances will only decompose when heated, this is known as thermal decomposition. Metal carbonates and metal hydrogen both undergo thermal decomposition when heated
When two soluble reactants combine to form an insoluble product known as the precipitate
(double displacement
ab + xy = xb + ay
Metal + water
Alkali metals and alkaline earth metals react violently with water
Combustion
Reactive metals such as magnesium and sodium can also combust in oxygen
The combustion of hydrocarbons produce carbon dioxide and water
Combustion is any chemical reaction in which a substance burns in oxygen to produce heat and light (exothermic) in some reactions the energy is converted into other forms of energy such as electrical
When reactions have limited oxygen it produces carbon monoxide and sooty carbon (incomplete combustion)
Metal + oxygen
Metal + oxygen = metal oxide
The most common example of corrosion is rusting of iron and its alloys
Most metals will combine with oxygen gas in the air to form metal oxides this is known as corrosion