BONDING OF ELEMENTS

Predict Why do elements bond? Why are valence electrons so important?

How does bonding occur? Chemical bonding – the combining of atoms of elements to form new substances. The rules of chemical bonding are determined by the structure of the atom. The outermost energy level determines if it will bond or not. Valence electrons – the electrons in the outermost energy level of an atom.

Energy levels Electron energy levels: 1 st – 2 2 nd – 8 3 rd – 18 4 th - 32

Electrons and bonding…

STABILITY Atoms with a complete outermost level (8 valence electrons) are very stable. They do not bond with other atoms. Each atom tries to reach stability by losing or gaining electrons. 1, 2, 3 = lose electrons 5,6,7 = gain electrons 4 = gain or lose 8 = unresponsive

Bonding Prediction When an element has a low number of valence electrons, in order to achieve the magic number of 8, are the electrons given away or are more taken?

Ionic bonding Ionic bonding – involves a transfer of electrons. One atom gains and the other one loses. Ion – a charged atom (positive or negative). Example: Fluorine (F) has 7 valence electrons and to become stable, it gains one electron to fill its outermost level and becomes a negative ion.

Ionic Bonding

+ - Na Cl Illustrating the bonding of Sodium and Chlorine

Sodium (Na) 11P 12N Sodium Na = 2,8,1 Sodium is soft and very reactive metal It has only 1 electron in its outside shell

Chlorine (Cl) 18P 17N Chlorine Cl = 2,8,7 Chlorine is a highly poisonous green gas. It has 7 electrons in the outside shell and is not stable.

Neither sodium nor chlorine are stable, since both have less than 8 electrons in their outside shell. However this can easily be achieved by combining Na and Cl together. 17P 18N 11P 12N NaCl Watch how!

Na is giving away its 1 electron which it has in its outside shell …. 17P 18N 11P 12N NaCl

Cl is accepting the electron from Na 17P 18N 11P 12N Na Cl

Both Na and Cl now have 8 electrons in their outside shell and a new compound NaCl has been formed 17P 18N 11P 12N Na + 2,8 Cl- 2,8,8

Both Na and Cl now have 8 electrons in their outside shell and a new compound NaCl has been formed 17P 18N 11P 12N Na+ 2,8 Cl- 2,8,8 Strong forces of attraction exist between Na+ and Cl- and hold the bond together

Satisfying the Octet Rule….. The Octet rule is simply a rule which helps us to understand bonding Atoms bond together so that each atom attains an electron arrangement of 8 electrons in its outermost shell. The Octet Rule :

To satisfy the Octet Rule, atoms tend to gain, lose or share electrons Na lost 1 electron Na changed from electron configuration of 2,8,1 to 2,8 Na changed from a neutral Na atom to a positively charged Na ion (Na+) Cl gained 1 electron Cl changed from electron configuration of 2,8,7 to 2,8,8 Cl changed from a neutral Cl atom to a negatively charged Cl ion (Cl-)

Difference between the sodium and the sodium ion The sodium atom 11 Protons (11+) 12 neutrons 11 electrons (11-) The sodium ion 11 Protons (11+) 12 neutrons 10 electrons (10-) The sodium atom Na has an equal number of + and - charges The sodium ion Na has an extra one + charge Na+ An ion is a charged atom

Chlorine and the chloride ion The chlorine atom 17 Protons (17+) 18 neutrons 17 electrons (17-) The chloride ion 17 Protons(17+) 18 neutrons 18 electrons (18-) The chlorine atom Cl has an equal number of + and - charges The chloride ion Cl has an extra one “- “charge Cl- An ion is a charged atom

Atom processes Ionization – the process of removing electrons to form ions. The energy needed is called ionization energy. This is low if there are few valence electrons (1, 2, or 3); and it is high if there are many valence electrons (5, 6, or 7).

Electron affinity – the tendency of an atom to attract electrons.

Crystal formation… DIAMOND Crystal shapes are due to the placement of ions in a repeated pattern.

Diamonds…

More bonding!!!!!!

Predict again Would it be easier to take an electron or 2 to bond or share?

Covalent bonding Covalent bonding – occurs between atoms that have high ionization energy and high electron affinity. They share electrons, rather than transfer. “Co” means to share. Simplest example: Hydrogen H : H

Hydrogen(H) 1P 0N Hydrogen H= 1 Hydrogen is a gas. Hydrogen has only 1 electron in its outer shell

Chlorine (Cl) 18P 17N Chlorine = 2,8,7 Chlorine is a poisonous gas. It has 7 electrons in the outside shell and is not stable.

Neither Hydrogen nor Chlorine are stable, since both have less than 8 electrons in their outside shell. However this can easily be achieved by combining H and Cl together. 17P 18N 1P 0 N HCl Watch how!

A covalent bond will be formed between H and Cl by sharing a pair of electrons …. 17P 18N 1P 0N H Cl A Hydrogen atom has only 1 electron which it cannot lose. Therefore, the only type of bond H can form is a covalent bond

HCl 17P 18N 1P 0N H Cl 1 atom of Hydrogen has combined with 1 atom of Chlorine. Both H and Cl are now in a stable state - each with a full outer shell.

Satisfying the Octet Rule….. The Octet rule is simply a rule which helps us to understand bonding Atoms bond together so that each atom attains an electron arrangement of 8 electrons in its outermost shell. The Octet Rule :

To satisfy the Octet Rule, atoms tend to gain, lose or share electrons The H began with 1 electron in its outer shell - It needed 2. The Cl atom began with 7 electrons in its outer shell - It needed 8. H and Cl shared one pair of electrons By sharing the pair of electrons, both atoms are now in a stable state. H has 2 electrons in its outer shell and Cl has 8 in its outer shell.

H 1P 0N 1P 0N H H 1 atom of Hydrogen has combined with 1 atom of Hydrogen. Both Hydrogens are now in a stable state - each with a full outer shell. 2 Other examples of Covalent Bonds

The Water molecule 1P 0N 8P 8N O H H 2 1P 0N O H

COVALENT BONDING

More about covalent bonds… Covalent bonds form molecules. A molecule is the smallest particle of a covalently bonded substance that shares all the properties of that substance. Example: one molecule of water.

Other types of bonding… Metallic bonding – bond when the positive nuclei are surrounded by mobile electrons. (all attracted at the same time). This allows the metals to be heat conductors. This is when the electrons are able to come off of their electron orbits and move freely.

“Sea of Electrons”

Predicting types of bonding… Ionic – elements lose or gain electrons easily (metals/non-metals). Covalent – similar tendency to gain electrons, bond betweens non-metals. Metallic – bonds between mostly transition metals, gives them the power to conduct electricity.

Polyatomic ion – when two elements bond first covalently and then the two of them bond as a single unit to another element through ionic bonding. (both types of bonding have occurred).

Oxidation # Oxidation number – the number of electrons an atom gains or loses, or shares in a chemical bond. Example: Na (1 val. electron) Loses it. +1 oxidation # *If the sum of oxidation number is zero; they will bond. Ex. Chlorine (-1) and Sodium (+1) = 0

Oxidation Numbers An electron donor becomes positive An electron acceptor becomes negative Ca looses two electrons so it has an oxidation number of 2+ Ca²+ Cl gains an electron so it has an oxidation number of 1- Cl¹- In bonding it takes 2 Cl to bond to 1 Ca to become a neutral compound CaCl 2

Diatomic elements Diatomic elements – form bonds with atoms of the same element. Examples: H, Cl, O, F, Br, I, N, C

I can see you understand!!