IONS AND BONDINGYou will notice that not all the atoms have fully filled outer valence shell from the belowdiagram which only shows the number of electrons in the valence shell.Is there a pattern you see here?Also notice that the last column (He and Ne) are known as unreactive noble gases, why doyou think that is so?For the pattern,The number of valence shell electrons remain the same down a groupFor the last column, noble gases have octet electronic configuration, therefore they do notneed to react with other atoms to be stableHelium does not have 8 electrons in its outer shell, it only has 2 so for helium we say it hasduplex electronic configurationWhereas all the other noble gases have 8 electrons in their valence shells and hence, can bedescribed has having octet electronic configuration.All atoms like to have fully filled valence shells, this is very important.
Notice that group 1-3 fall under metalsWhile group 4 to 8 fall under non-metalsBecause metals have fewer valence electrons, they prefer to give away their valenceelectrons and enjoy the stability provided by an octet electronic configuration.What happens when an atom gives away electrons?Notice that a sodium atom has 11 protons and that number of protons will never change. Butyet if it has given 1 electron away, how many electrons does it have left? _____What happens is sodium has 1 more proton than electron, and we know that protons have apositive charge of +1 And that atom changes from being neutral to being an ion that has a charge of +1 As the diagram shows, a +1 ion produces an electrostatic field that can attract or repel other charged particles!
Solidify your understanding!1) what is the ion formed by atoms of magnesium, boron, and lithium when they lose theirelectrons?_________________________For non-metals, they can get a octet valence shell through 2 waysThe first way is to gain electrons.Nitrogen needs to gain ____ more electrons to reach octet configuration.Oxygen needs to gain ____ more electrons to reach octet configuration.Similar to the example on sodium above, when a non-metal atom such as fluorine atom gainsan electron, suddenly it has 10 electrons and only 9 protons and it has become an ______ witha charge of -1Solidify your understanding!1) what is the ion formed by atoms of chlorine and sulphur when they gain some electrons?____________________2) what is the electronic configuration of sulphide (S2-) and oxygen ion?____________________________________________But in order to gain electrons, non-metal atoms need to come into contact with ___________atoms.The transfer of electrons from metal to non-metal atoms results in ions of opposite chargesbeing formed. Unlike charges cause them to be attracted strongly to each other.
Obtaining the formula for ionic compoundsAn ionic compound is always made up of _______ positively charged ions and_________________ negatively charged ions.The total charge of the ions always equal to zero, because the number of electrons given toform the positive ions is equal to the number of electrons gained to form the negative ions3 simple steps to follow to get the formula of an ionic compound1. Determine the charge of the metal positive ion using the periodic table2. Determine the charge of the non-metal negative ion using the periodic table3. Find the LCM of both charges to get the numbers of each ion in the compoundTry to find out the formula of 1) Magnesium Chloride and 2) Lithium Oxide_______________________________________________________Harder example: try to find the formula of Aluminium Oxide______________________________________________________There are also some ions which are not found in the periodic table such as ammonium ionwhich is NH4+, andsulphate ion which is SO42-, as well as nitrate NO3- and carbonate CO32-.Find out the chemical formula of ammonium sulphate ___________________Take note that in your formula, the metal ion should always be first (such as NaCl) and bigions like sulphate or nitrate should be in brackets like in Mg(NO3)2.COVALENT BONDINGA covalent bond is defined as the sharing of a pair of electrons between two atoms. Andtake note that covalent bonds only apply to non-metal atoms.Below are a few examples
This is CH4Now you can try to form dot-and-cross diagrams of the following molecules, do not forget toinclude a legend, which is worth marks in exams!1. F2Some of the harder ones involve many atoms so you need to know which atoms are in thecentre of the molecule. The more number of covalent bonds an atom need to get octetconfiguration, the more likely it is to be in the centre bonding to many other atoms.1. N2 2. NH3Atoms and moleculesMolecules refer to two or more atoms covalently bonded together
IONS AND BONDING CHECKLIST1) Identify the group that the following elements belong toAluminium Group 3 Bromine NeonLithium Magnesium PhosphorousSulphur Beryllium OxygenHelium Sodium Boron2) Draw a dot and cross diagram of sodium fluoride showing all the electrons.3) Draw a dot and cross diagram of HCl showing all the electrons
4) Magnesium ion has a charge of +2 and oxide ion has a charge of +2, why is MagnesiumOxide’s formula not MgO2?1) 1 Mg and 1 Oxide ion balance out with a net charge of +2.2) 1 Mg and 1 oxide ion balance out with no net charge3) 1 Mg and 2 oxide ion do not balance out, there is a net charge of +24) 1 and 3 are correct5) 2 and 3 are correct5) Draw a dot and cross diagram of H2O showing only the valence electrons