Chemical Bonding

Ionic Bonds Ionic bonds are made between metal and non-metal atoms Electrons are transferred from the metal atom to the non-metal atom Metal atoms lose electrons form positive ions called cations. Non metal atoms gain electrons form negative ions called anions.

Metals Metal atoms lose electrons to form positive ions (an atom that loses or gains electrons) called cations. E.g., Beryllium (Be) Group 2 Neutral atom Positive ion4+ P’s 4- E’s2- E’s 02+ Valence Electrons The electrons in the outer shell of an atom, which determines its power to combine with other elements

Non-metals Non-metal atoms gain electrons to form negative ions called anions. E.g., Carbon (Ca) Group 14 Neutral atom Negative ion6+ P’s 6- E’s10- E’s 04-

Let us consider the bonding in the substance sodium chloride. Na + + Cl - Na + Cl - In this reaction the sodium (Na) atom loses 1 electron while the chlorine atom accepts the electron in the transfer process. An example of ionic bonding…..

NaCl Thus we can say that sodium chloride is an ionic compound

Ionic Compound – A compound that contains positively charged ions and negatively charged ions. Ionic Compounds

NaCl Na+ Sodium ion This charged atom contains: 11+ Protons +10- Electrons - 1 Cl- Chloride ion This charged atom contains: 17+ Protons +18- Electrons +1

Sodium Chloride Thus NaCl Once these two ions (An atom that has become charged be gaining or losing one or more electrons) have been formed, they will attract each other because of their opposite charges

CaO Ca 2+ + O 2- Ca 2+ O 2- In this reaction the calcium (Ca) atom loses 2 electrons while the oxygen (O) atom accepts the two electrons in the transfer process.

Thus we can say that calcium oxide is an ionic compound

Calcium Oxide Ca 2+ Calcium ionO 2- Oxide ion 20+ Protons8+ Protons 18- Electrons10- Electrons Once these two ions have been formed, they will attract each other because of their opposite charges. There is an electrostatic attractive force present (like charges repel and unlike charges attract) that creates the chemical bond in the NaCl and CaO called an ionic bond.

Let’s try one….. One example is sodium (Na) and fluorine (F) Each atom wants to become stable (more like the noble gases!) This means that Na wants to lose one eˉ and F wants to gain one eˉ This process of electron rearrangement explains the formation of compounds such as sodium fluoride (NaF) Chemical Name: Sodium Fluoride Chemical Formula:

Another example..... Magnesium and Fluorine Metal Non-metal 12+ Protons9+ Protons10- Electrons Mg 2+ + F 1- Mg 2+ F 1- Chemical name: Magnesium fluoride Chemical Formula: MgF 2

Metals tend to form cations Non-metals tend to form anions. Predicting Ionic Charge

The group number on the periodic table indicates the number of electrons the atom will lose or gain. Group 1 elements form cations with one positive charge. Group 2 elements form cations with two positive charges. Group 3 elements form cations with three positive charges. Group 17 elements form anions with one negative charge. Group 16 elements form anions with two negative charges. Group 15 elements form anions with three negative charges.

Figuring out Ionic Charge For metals, it‘s the same as the group number (the column number). For non metals, the charge is equal to whatever number needs to be added to the group number to get 8. Group 8, (the noble gases), don‘t form ions as they do not need to gain any electrons to have a full outer shell

Naming Ionic Compounds Usually, the cation (positive ion) is written before the anion (negative ion) The first word is the name of the element where the cation originally came from The last word is the name of the anion with the suffix “ide”

More to try…….. Potassium and Sulfur Aluminium and Chlorine Aluminum and Oxygen Calcium and Fluorine

Bonding in Ionic Compounds According to the ionic electrostatic model, solids such as NaCl consist of positive and negative ions arranged in a crystal lattice. Each ion is attracted to neighbouring ions of opposite charge, and is repelled by ions of like charge; this combination of attractions and repulsions, acting in all directions, causes the ion to be tightly fixed in its own location in the crystal lattice. Sodium metal reacts with chlorine gas in a violently exothermic reaction to produce NaCl (composed of Na + and Cl - ions): 2Na(s) + Cl 2 (g) -> 2NaCl(s)

Crystal Lattice Strong forces between ions make these compounds very hard, therefore they are not good electrical conductors (ions are not able to move) They can however, conduct electricity when dissolved in water or heated above their melting point

Properties of Ionic Compounds PropertyIonic Compounds General DescriptionSolid at room temperature Forms crystal structures Usually hard but very brittle (break vs. bend) Melting PointGenerally quite high (eg. NaCl = 801°C) SolubilityHighly soluble in water Conductivity in Solid StateVery poor conductors Conductivity in Molten State (or dissolved)Excellent conductors Electrolyte (when dissolved) OdourUsually does not emit an odour in the solid state

Molecular Compounds Molecular compounds are made up of uncharged atoms When we looked at ionic compounds, we saw that atoms of metals and non-metals bonded by swapping electrons Molecular compounds occur when 2 atoms (both non-metals) combine by sharing their electrons This is called covalent bonding

Examples of Covalent Bonds This is a water molecule (H 2 O) In this case, the oxygen atom needs two more electrons, so two hydrogen atoms each share a pair of electrons with the oxygen atom

Properties of Molecular Compounds PropertyMolecular Compounds General DescriptionSolid, liquid, or gas at room temperature Forms crystal structures Usually soft at room temperature Melting PointGenerally low (compared to ionic) SolubilityInsoluble in water Conductivity in Solid StateVery poor conductors in any state Conductivity in Molten State (or dissolved)Poor conductors in any state OdourMany covalent substances emit a strong/distinctive odour at room temperature.

What is the difference? In general, the strength of covalent bonds is about the same as ionic bonds The difference is the attraction between molecules An ionic compound behaves like one large structure, with each ion surrounded by ions of opposite charge – strong attraction through the crystal In molecular compounds, the bonding between atoms is strong but the attraction between molecules is weak.