Chemical bonds

Chemical Bonding.

Unions that build

Atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell giving them the same electronic configuration as a noble gas.

The rule is applicable to the main-group elements, especially carbon, nitrogen, oxygen, and the halogens, but also to metals such as sodium or magnesium.

In simple terms, molecules or ions tend to be most stable when the outermost electron shells of their constituent atoms contain eight electrons.

The octet rule does not work for predicting the charges on transition metals ions.

Transition metals are located on the periodic table in the ten columns between columns for the representative elements, and the groups are labeled IB to VIIIB.

The transition metals typically produce ions with 1+, 2+, 3+ and sometime 4+ charges, and unlike the representative elements many transition metals can have more than one charge state

Valence electrons: Electrons in the outermost electron shells, maximum 8 electrons. noble gases has 8 electrons

Ion: A charged atom. Can be either positive or negative.◦ Positive ion: Is an atom that lost at least one

electron, are called cations. Example Na+, Mg2+, Al3+

◦ Negative ion: Is an atom that gained at least one electron, are called anions. Cl-, O2-, N3-

Groups IA, IIA, and IIIA have metallic atoms that tend to lose electrons to acquire electronic configuration of a noble gas forming positive ions.

Groups VA, VIA, VIIA have non metallic atoms that tend to gain electrons to acquire electronic configuration of a noble gas forming negative ions.

Element Group Valence e-

Electrons to form Ion

Ion Form

edLost Gained

Sodium IA Na+

Magnesium

IIA Mg2+

Calcium IIA Ca2+

Aluminum IIIA Al3+

Sulfur VIA S2-

Oxygen VIA O2-

Chlorine VIIA Cl-

Bromine VIIA Br-

Lewis structures, also called Lewis-dot diagrams, Electron-dot diagrams or Electron-dot structures, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule.

Consists of the element symbol surrounded by "dots" to represent the number of electrons in the outer energy level (correlated by the Group number).

However, because of the high charge that would result, either C4+ or C4- for carbon and Si4+ or Si4- for silicon

Lithium Calcium Aluminum Carbon Nitrogen Oxygen Chlorine Argon

Lithium ion Calcium ion Aluminum ion Carbon Nitrogen ion Oxygen ion Chlorine ion Argon

Symbol

Atomic Electronic configuration

Lewis atom structure

Formed ion

Ionic Electronic configuration

Lewis ionic structure

Li 1s2 2s1 Li Li+ 1s2 Li+

Be

B

C

N

O

F

Ne

A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei or as the result of a dipole attraction.

The strength of bonds varies considerably; there are "strong bonds" such as covalent or ionic bonds and "weak bonds" such as dipole-dipole interactions, the London dispersion force and hydrogen bonding.

Type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. It is a bond formed by the attraction between two oppositely charged ions, The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond like magnets .

The metal donates one or more electrons, forming a positively charged ion or cation with a stable electron configuration. These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration.

For example, common salt is sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron forming a cation (Na+), and the chlorine atom gain an electron to form an anion (Cl−).

Na + Cl Na+ + Cl-

Formed between a metallic element and a non metallic element.

The bonding involves electrons transfer, the metal atom donates electrons while the non metal accept the electrons.

The compounds formed are solids with a crystal lattice tridimensional structure.

Most of them dissolve in water giving solutions that conducts electricity

Salts (NaCl) and acids (HCl) are ionic compounds

1. Find the total number of electrons:For each atom, read the group number.

2. Draw a first tentative structure: The element with the least number of atoms is usually the central element. Draw a tentative molecular and electron arrangement attaching other atoms with single bonds as the first guess.

3. Add electrons as dots to get octets around atoms:When counting electrons for the octet around an atom, count both electrons in a bond for each atom and any lone pair electrons. Hydrogen, of course, gets only 2 electrons.

4. Count the total number of electrons in the final structure to see if the total agrees with the number tabulated in step #1. If not, then move a lone pair of electrons into a double bond. Or add more lone pairs of electrons.

5. Cycle through steps 3 and 4 several times until you get it right by trial and error.

NaCl Na IA = 1e Cl VIIA= 7e

Na + Na+

MgCl2 Mg IIA=2e Cl VIIA= 7e

Mg + Mg2+

RbBrCaBr2

AlF3

SrO

Cl

Cl -

Cl

Cl

Cl -

Cl -

Chemical bonding is characterized by the sharing of pairs of electrons between atoms.

Is formed by at least two non-metallic elements, they can be molecules of the same atom like O2 or different atoms like H2O.

The atoms can share more than one pair of electrons, they can share two or even three pair of electrons, like single, double or triple bonds.

or

The pair of shared electrons can be drawn with lines

Cl

Chlorine molecule Cl2 Cl = 7 e

Cl

pair of shared electrons in red, each chlorine atom has 8 e

Single: One pair of electrons are shared.

Double: Two pairs of electrons are shared.

Triple: Three pairs of electrons are shared

or

1. Write the valence electrons of the Nitrogen atom

2. Write the total number of electrons from both atoms

3. Draw the dot diagram4. Arrange the electrons using octet rule

(both atoms must have 8 electrons how many electrons must they share?)

N from family VA= 5 electrons For the molecule N2 are 10 electrons Sharing just one pair doesn’t apply the octet rule. Neither sharing two pairs of electrons apply

But sharing THREE pair of electrons the octet rule does apply or N N

N

N

N

N

N

N

N

N

F2

NH3

H2

H2S HBr CH4

CO2

CO O2

CCl4

Polar covalent: between atoms of different elements. Example H2O, H2S, CO2, CCl4. The type of bond is also determined by the difference of the electronegativity values of the elements <(below)1.7Example : H2O

H=2.1 O=3.5 3.5-2.1= 1.4 polar covalent bond

Non-polar Covalent: Between molecules. Same elements. Example H2, O2, Cl2, F2. The type of bond is also determined by the difference of the electronegativity values of the elements = 0Example F2

F= 4 4-4 = 0 Non-polar Covalent bond

Compound

Electronegativity value of each

atom

Electronegativity difference

Type of bond

F2 F: 4.0 F: 4.0 4.0 – 4.0 = 0 Covalent Non-polar

H2S

NaF

RbBr

NH3

HF

MgO

KCl

N2

CH4

In chemistry, polarity refers to a separation of electric charge leading to a molecule having an electric dipole.

Polar: Is a molecule that can dissolve in water like Salts (NaCl, KF, etc) and Acids (HCl, HNO3, etc).

Non polar: Is a molecule that can not dissolve in water like fats, oils, gasoline, methane gas (CH4) carbon tetrachloride (CCl4), CO2.

A water molecule, a commonly-used example of polarity. The two charges are present with a negative charge in the middle (red shade), and a positive charge at the ends (blue shade).

Metallic bonding is the electromagnetic interaction between delocalized electrons, called "electrons sea“.

The electrons sea are the responsible for the physical properties of solid metals: conduct heat and electricity, generally high melting and boiling points,strong, malleable (can be hammered or pressed out of shape without breaking), ductile (able to be drawn into a wire), metallic lustre

The elements involved in this type of bonding are mainly the transition metals like Fe, Cu, Au, Ag, Al, Zn, Pt, etc.

Are the forces holding molecules together◦Dipole-dipole forces◦Weak London dispersion or van der Waal's force. ◦Hydrogen bond

Certain substances such as H2O, HF, NH3 form hydrogen bonds, and the formation of which affects properties (solubility) of substance. Other compounds containing OH and NH2 groups also form hydrogen bonds. Molecules of many organic compounds such as alcohols, acids, amines, and aminoacids contain these groups, and thus hydrogen bonding plays a important role in biological science.

Which of the following pairs has the strongest hydrogen bond.

a)HCl or HFb)NH3 or PH3

c)H2O or H2S