Intro to Bonds

Intro to Bonds

Physical Science - Hendley

Valence Electrons

• Electrons orbit the nucleus (more-or-less) similarly to how planets orbit the sun.

• Electrons prefer lowest energy, so the first energy level (closest to the nucleus) will fill first.

• The first energy level can hold only TWO electrons.

• Electrons in the highest occupied energy level are called Valence Electrons and are important because they are the only electrons available for bonding.

Valence Electrons (cont.)

• Once two electrons go in the first energy level, more electrons will then fill in the 2nd energy level

• When drawing Lewis dot diagrams, put the element symbol and dots around it. (as shown on the right)

• Please note that Helium is a big exception. It only has 2 electrons, but they are paired to show they are unavailable for bonding. Helium does not form bonds!

Lithium

• Lithium has 3 total electrons (Atomic number = Z = 3)

• The first two go in the first energy level

• The third electron goes in the 2nd energy level

• When drawing the Lewis dot diagram, only the valence electrons are represented.

Carbon

• Carbon has 6 total electrons (Z = 6)

• The first two go in the first energy level

• The next four go in the 2nd energy level

• When drawing the Lewis dot diagram, these four valence electrons are spaced out, one per side of an imaginary square. These "single" or "unpaired" electrons show the potential for bonding.

Oxygen

• Oxygen has 8 electrons total (Z=8)

• The first 2 fill the first energy level

• The next 6 go into the 2nd energy level, 2 paired and 2 unpaired.

• This helps predict that oxygen will form bonds. Or, that it needs 2 more electrons to complete its octet.

Neon

• Neon has 10 electrons total. (Z=10)

• The first two fill the 1st energy level.

• The other eight fill the 2nd energy level.

• Neon is a Noble gas and does not react with other elements because it does not need any electrons, nor does it have a surplus of any.

Sodium

• Sodium has 11 total electrons. (Z=11)

• The first two fill the 1st energy level.

• The next eight fill the 2nd energy level.

• The last one occupies the 3rd energy level.

Multiple Choice

How many electrons can fit in the 2nd energy level?

• 2

• 8

• 16

• 18

Multiple Choice

How many electrons can fit in the 3rd energy level?

• 2

• 8

• 16

• 20

Multiple Choice

Valence electrons refer to the

• total number of electrons

• electrons in the completed energy levels.

• electrons in the outermost energy levels.

• electrons that are paired together.

The Octet Rule

• The octet rule states simply that atoms will gain, lose or share electrons in order to have eight valence electrons.

• There are some exceptions to this (like Hydrogen only wants 2 because it only has the first energy level) but this rule is a good rule of thumb.

Multiple Choice

How many valence electrons do most atoms want/need?

• 1

• 2

• 6

• 8

Ionic Bonds

For many atoms, the best way for them to get stable is to either gain or lose electrons to reach an octet.

Sodium has 1 valence electron, so it is 'easier' for it to lose that one and revert to a full 2nd energy level.

Fluorine has 7 valence electrons and needs one more to complete the octet. It eagerly accepts that electron.

Ionic Bonds (cont.)

When sodium loses the 1 valence electron, it then has 11 protons (still Sodium!) and only 10 electrons, giving it a 1+ charge.

(For charges, we right the sign second because it reads as "1 unit of + charge")

Fluorine has 9 protons (Z=9) but now 10 electrons, so it has a 1- charge.

Ionic Bonds (cont. 2)

Because sodium has a 1+ charge and fluorine has a 1- charge, the opposite charges cause them to attract in a 1:1 ratio to reach electrostatic neutrality.

Positive ions are called cations.

Negative ions are called anions. Their ending is also changed to -ide.

Metal ions

• Metals are, in general, loosely attracted to their valence electrons. They're large atoms and the valence electrons are far from the positive protons in the nucleus.

• Because metals lose electrons, they form positive ions called cations.

• When naming cations, do not change their name.

• In the picture, there is a sodium atom on the left and a sodium ion on the right after it has lost its 1 valence electron.

Multiple Choice

When forming ions, metals form

• cations, which are positive.

• cations, which are negative.

• anions, which are positive.

• anions, which are negative.

Nonmetal ions

• Nonmetals are, in general, strongly attracted to their valence electrons. They're relatively small atoms and the valence electrons are fairly close to the positive protons in the nucleus.

• Because nonmetals gain electrons, they form negative ions called anions.

• When naming anions, change their ending to -ide.

• In the diagram, oxygen is depicted (Z=8). The valence shell has 6 electrons, so it needs 2 more electrons to complete the octet, giving it a 2- charge and the oxygen atom on the left becomes the oxide ion on the right.

Multiple Choice

When forming ions, nonmetals form

• cations, which are positive.

• cations, which are negative.

• anions, which are positive.

• anions, which are negative.

Multiple Choice

Will magnesium likely gain or lose electrons when forming an ion?

• gain

• lose

• impossible to predict

Multiple Choice

Will strontium likely gain or lose electrons when forming an ion?

• gain

• lose

• impossible to predict

Multiple Choice

Which set of atoms will most likely form an ionic bond?

• H and Cl

• H and H

• Li and F

• Mg and Al

Covalent Bonds

• Covalent bonds are when electrons are shared between two elements and are most likely to form between two nonmetals.

Nonmetals share electrons

• Nonmetals will share electrons with one another in order to complete their octet.

• Remember: Hydrogen only needs one more electron to complete the first energy level. (not pictured)

• Nonmetals in Group 15 have 5 valence electrons and need 3 more to complete.

• Nonmetals in Group 16 have 6 valence electrons and need 2 more to complete.

• Nonmetals in Group 17 have 7 valence electrons and need 1 more to complete.

Covalent Bonds

• Only the unpaired valence electrons are normally involved in bonding.

• So, oxygen typically only forms 2 bonds, carbon will form 4 and the halogens only 1.

• Sometimes, atoms may need multiple electrons and can form a double bond (2 pairs of electrons) or even a triple bond (3 pairs of electrons).

Multiple Choice

As a bond between a hydrogen atom and a sulfur atom is formed, electrons are

• shared to form an ionic bond.

• shared to form a covalent bond.

• transferred to form an ionic bond.

• transferred to form a covalent bond.

Metallic Bonds

• Metals are loosely attracted to their valence electrons and easily share them amongst one another.

• When metals bond with metals, their electrons are delocalized and shared by all of the other atoms in a "sea of electrons."

• These flowing electrons allow metals to be good conductors of electricity, as well as malleable and ductile.

Multiple Choice

What sort of bond would form between two metals?

• Ionic bonds

• Hydrogen bonds

• Covalent bonds

• Metallic bonds

Multiple Choice

How many electrons does barium have to give up to achieve a noble-gas electron configuration?

• 1

• 2

• 3

• 4

Multiple Choice

How many valence electrons does a helium atom have?

• 1

• 2

• 6

• 8

Multiple Choice

Which formula represents an ionic compound?

• $$CH_3OH$$

• $$CH_4$$

• $$NH_4Cl$$

• $$H_2$$

Multiple Choice

Each molecule of table sugar contains

$$C_{12}H_{22}O_{11}$$  

• 6 atoms of carbon

• 1 atom of carbon

• 12 atoms of carbon

• 0 atoms of carbon

Multiple Choice

Valence electrons determine an atom's

• mass.

• chemical properties.

• period.

• electric charge.

Multiple Choice

Which element will most likely form covalent bonds with chlorine?

• magnesium

• aluminum

• potassium

• carbon

Multiple Choice

The compound sodium chloride is placed in water and separates into ions. What are the correct names for these ions?

• The sodium ion is the cation; the chloride ion is the anion.

• The sodium ion is the anion; the chloride ion is the cation.

• The chloride and sodium ions are anions.

• The chloride and sodium ions are cations.