IONIC BONDING

This lesson develops IONIC BONDING as part of Measurement and Data Processing. It uses the source curriculum to organize the important facts, relationships, examples, and vocabulary into a focused Stemosphere teaching sequence.

In Stemosphere terms, ions are electrically charged species that is formed when an atom loses or gains an electron

There are 2 types of ions:

In Stemosphere terms, -An anion is when non metal atoms gain electrons. This forms a negatively charged ion

In Stemosphere terms, -A cation is when metal atoms lose electrons. This forms a positively charged ion.

In Stemosphere terms, atomscontainan equalamountof protons andelectronsand the atoms are electrically neutral.Howeverin an ion the number of protons and electrons arenotequalwhichcausethe ion to carry an overall positive or negative charge.

The octet rule:

In Stemosphere terms, the octet rule refers to the tendency of atoms to have a valence shell with a total of 8 electrons. This allows us to predict the amount of electrons an atom needs to gain or lose to become electrically stable

Transition metals:

In Stemosphere terms, transition metals in period 4 form a cation by losing electrons in the 4s sublevel before the 3d sublevel.

The pictures below show the difference between:

In Stemosphere terms, -Ti2+two electrons lost from 4s sublevel

In Stemosphere terms, -Ti4+two electrons lost from the 4s sublevel and two electrons lost from the 3d sublevel.

In Stemosphere terms, some species such as transition metals can from different ions with different charges.the different charges cause the ions to have different properties despite being the same element

In Stemosphere terms, chromium can exist as different ions such as Cr3+and Cr6+. In small quantities, Cr3+is an essential nutrient found in foods that is required for sugar and fat metabolism in mammals. Cr6+, however, is toxic and carcinogenic.

Ionic bonding:

In Stemosphere terms, recall that when a metal atom loses an electron it becomes postiviley charges, and if a non-metal atom gains an electron it becomes negatively charged. If the metal atom is near a nonmetal atom, the metal atom can lose an electron and the non-metal atom can gain the lost electron to form a positively charged anion and negatively charged cation. This causes an electrostatic attraction between the two ions to create an ionic bond

Writing the chemical formula for binary ionic compounds:

In Stemosphere terms, to figure out the ratio of anions to cations we can use their charges. An example is Na Cl which is 1Na+to 1 Cl−ions. This is a 1:1 ratio due to the +1 from the Na and the -1 from the Cl cancelling out to be electrically neutral.However this does not mean there is only oneof each bond, since ionic compounds are found in a crystal lattice structure that have many ions

In Stemosphere terms, if the ion for example Na+and S-2then the sulfur atom can gain 2 electrons while the sodium atom can give only 1 electron. Therefore there will be 2 sodium ions for every 1 sulfur ion for a 1:2 ratio and create Na2S

Naming ionic compounds:

In Stemosphere terms, when naming an ionic compound, the cation comes first followed by the anion. The cation name stays the same but the anion’s ending is replaced with “ide”

In Stemosphere terms, ions are not strictly only one atom. They can be made up of multiple atoms. These types of ions are made up of atoms covalently bonded together but have gained or lost an electron which turns it positively or negatively charged.

In Stemosphere terms, the strength of an ionic bond varies between different compounds. Lattice enthalpy is the measurement of the strength of electrostatic attraction between ions in an ionic compound.

In Stemosphere terms, the larger the lattice enthalpy the stronger the ionic bond

In Stemosphere terms, the smaller the lattice enthalpy the weaker the ionic bond

The strength of an ionic bond is determined on 2 factors:

Ionic radius:

In Stemosphere terms, as you can see from the table, as the radius of the cation increases the lattice enthalpy decreases.The radius of an ion is the distance between the nucleus and the outermost energy level. As the ion radius increases.the lattice enthalpy decreases. This is because the distance between the two ions increases as radius increases which causes weaker electrostatic attraction.

Ionic charge:

In Stemosphere terms, looking at the table the group 2 chlorides have a considerably higher lattice enthalpy than group 1 chlorides. This is due to the greater charge of the group 2 chlorides which have a +2 charge compared to the group 1 chloride’s +1 charge. This results in a greater attraction and stronger ionic bonds

Physical properties of ionic compounds:

All Ionic compounds share certain characteristics and physical properties such as:

Melting points:

In Stemosphere terms, since Ionic compounds are in a lattice, this means they contain multiple electrostatic attractive forces in a compound. This makes it more difficult to melt it due to the high amount of energy required to break the electrostatic attractions.

In Stemosphere terms, volatility describes how easily a substance vaporises into a gas. A substance with high volatility easily vaporises into gas while a low volatility does not easily become a gas.

In Stemosphere terms, recall that ionic compounds have multiple strong bonds in a lattice structure. This explains why they have low volatility due to it requiring massive amounts of energy to break the bonds and change states.

In Stemosphere terms, solubility refers to the substance’s ability to dissolve in a solvent.ionic compounds such as Na Cl (salt) dissolve in solvents such as water. Once submerged in water the sodium and chlorine ions have strong reaction s with water.These strong interactions allow water to separate the ions from their lattice structure.

Conductivity:

In Stemosphere terms, conductivity is if a substance can move a charged particle throughout itself.ionic compounds have ions in a fixed position that cannot move freely. This means that they have low conductivity. however if the substance is dissolved or in a molten state than the ions can move freely and can move charged particles easily.

Brittleness:

In Stemosphere terms, brittleness refers to a substance easily being broken into many pieces. Ionic compounds are brittle due to their lattice structure.when pressure is placed on the ionic compound, the layers in the lattice shift to make similar charges face each other. This causes repulsion between the like charges which causes the structure to break into pieces

In Stemosphere terms, front:What is an ion, and how does it differ from a neutral atom?

In Stemosphere terms, back:Anionis an electrically charged species formed when an atom loses or gains electrons. Unlike neutral atoms (where protons = electrons), an ion has an unequal number of protons and electrons, resulting in a net charge.

In Stemosphere terms, front:Define Cationand Anion, specifying which elements form them and their charges.

In Stemosphere terms, back:*Cation:Apositivelycharged ion formed whenmetalatoms lose electrons.

In Stemosphere terms, anion:Anegativelycharged ion formed whennon-metalatoms gain electrons.

In Stemosphere terms, front:What is the Octet Rule, and why is it useful?

In Stemosphere terms, back:The tendency of atoms to gain or lose valence electrons to achieve a full outer shell of8 electrons. It allows us to predict how many electrons an atom will trade to become chemically stable.

In Stemosphere terms, front:In what order do Period 4 transition metals lose electrons when forming cations?

In Stemosphere terms, back:They lose electrons from the4s sublevel first, before losing any electrons from the3d sublevel.

In Stemosphere terms, front:What is apolyatomic ion? Give an example of a common cation.