Forming compounds
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Forming Compounds. When two atoms collide, the valence electrons of each atom interact. Elements try to get to the electron configuration of the closest noble gas - full valence shell. Valence Shell. Three ways for an atom to acquire a full valence shell. An atom may give up electrons

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Forming Compounds

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Forming compounds

Forming Compounds

  • When two atoms collide, the valence electrons of each atom interact.

  • Elements try to get to the electron configuration of the closest noble gas - full valence shell.


Valence shell

Valence Shell

  • Three ways for an atom to acquire a full valence shell.

    • An atom may give up electrons

    • An atom may gain electrons

    • An atom may share electrons

  • When atoms give up and gain electrons in a reaction the resulting compound is known as an ionic compound with an ionic bond.

  • The third way to acquire a full valence shell will be talked about later in the course.


Ionic compounds

Ionic Compounds

  • Ionic compounds involve bonds between a metal cation and a non-metal anion.

  • If just two different elements are involved, than you have a binary compound.

  • Binary compounds require that the total charge (sum of the element’s charges) of the compound is equal to zero.

  • We represent the compound by writing down the element symbol for cation first and then the anion

  • Subscripts after each symbol identify how many ions are required for a total charge of zero.

  • The representation of the compound is known as the chemical formula


Lewis structures

Lewis Structures

  • Sodium (Na+) and Chlorine (Cl-)

  • Now Chlorine has a full valence shell and the ionic compound NaCl is formed.

Na

Cl

[ ]+

[ ]-

Na

Cl


Example

Example

  • NaCl (Table Salt)

  • How do we name this compound?

  • Sodium Chloride

  • The suffix “ide” is put at the end of the name for the element that is the electron acceptor (anion)

    Na+ + Cl- NaCl

  • The sodium has a +1 charge and the chlorine has a -1 charge therefore +1 + -1 = 0.


Another example

Another Example

  • What would happen if we combined Magnesium and Chlorine?

  • Charges do not add up to zero.

  • Therefore we need more of one of the elements, but which one.

  • Magnesium has a 2+ charge and Chlorine has a 1- charge so we need two Chlorine.

  • MgCl2 (Magnesium Chloride)

  • Can also be done by drawing out the required number of atoms to get a total charge of zero.


Polyatomic ions

Polyatomic Ions

  • Polyatomic Ions consist of two or more non-metal atoms grouped together.

  • There is only one common polyatomic cation

    • Ammonium NH4+

  • There are several common polyatomic anions

    • Hydroxide OH-

    • Carbonate CO32-

    • Nitrate NO3-

    • Sulfate SO42-

    • Chlorate ClO3-

    • Phosphate PO43-


Polyatomic i ons

Polyatomic Ions

  • Compounds are named the same way

  • Writing the chemical formula is a little different - If more than one polyatomic ion is needed, than brackets must be put around the ion

  • Example: The chemical formula for ammonium oxide is (NH4)2O not NH42O

  • Do not forget the brackets!!!!


Polyatomic example

Polyatomic Example

  • Calcium Nitrate

  • Calcium (Ca2+) and Nitrate (NO3-)

  • Need two Nitrate ions to balance charges.

  • Ca(NO3)2


Transition metals

Transition Metals

  • Transition metals can form more than one ion - except for silver(+1), zinc (+2) and aluminum (+3).

  • For example Sodium can only produce the Na+ ion. Iron on the other hand can produce two ions.

    Fe  Fe2+ or Fe3+

  • A roman numeral is placed after the atom in brackets to identify the charge

  • Iron that produces the +2 ion is iron(II)

  • Iron that produces the +3 ion is iron(III)


Examples

Examples

  • 1. Iron(III) Oxide (Rust)

    Fe3+ O2-

    Fe3+ O2-

    O2-

  • Charge of +6 from the iron and -6 from the oxygen. Chemical Formula - Fe2O3

  • 2. CuCl2

    Cu Cl-

    Cl-

  • Cu must have a +2 charge to balance the -2 from the 2 Cl. Copper(II) Chloride


Covalent bonds

Covalent Bonds

  • Two or more non-metallic elements.

  • Electrons must be shared since both atoms are looking to gain electrons.

  • When atoms share electrons they are joined by a covalent bond.

  • A neutral particle that is composed of atoms joined together by covalent bonds is called a molecule.

  • Substances that are composed of molecules are called molecular compounds.


Molecular compounds

Molecular Compounds

  • Water (H2O)

  • Two H+ atoms and a O2- atom.

O

H

H

O

H

H


Naming molecular

Naming Molecular

  • H2O

  • Start with the element that is farther left on the periodic table (Hydrogen).

  • The rules for the second element still apply, suffix of “ide”.

  • Different is that the elements require prefixes depending on how many are in the compound.

  • So water’s chemical name is dihydrogen monoxide.


Prefixes

Prefixes

  • Prefix mono is only used for the second element.

  • “a” or “o” is left off of the prefix when used with an element starting with a vowel


Diatomic molecules

Diatomic Molecules

  • Atoms can share electrons with the same atom.

  • These molecules have two of the same atoms joined by a covalent bond.

  • Since there are two of the same atoms the word diatomic is used. (“di” meaning two)

  • Seven elements exist as diatomics:

    • Hydrogen

    • Oxygen

    • Nitrogen

    • Fluorine

    • Chlorine

    • Bromine

    • Iodine


Ionic compounds1

Ionic Compounds

  • Ionic compounds form large structures called lattices

  • Attraction between oppositely charged ions is strong.


Ionic properties

Ionic Properties

  • Characteristics of an ionic compound:

    • Tend to have relatively high melting and boiling points because of the large amount of energy is needed to break the strong force of attraction in an ionic bond.

    • Conduct electricity when they are liquid or when they are dissolved in water. Melting or dissolving allow ions to move freely. In a solid state the ions are not able to move and therefore cannot conduct electricity.


Molecular compounds1

Molecular Compounds

  • Bonds within the molecule are strong but forces of attraction between the molecules is weak.


Molecular properties

Molecular Properties

  • Characteristics of a molecular compound:

    • Have relatively low melting points because little energy is needed to break the forces of attraction between molecules.

    • Relatively soft

    • Tend not to conduct electricity when they are in solid or liquid state. Do not conduct when dissolved in water because ions are not formed.


Electrolytes

Electrolytes

  • An electrolyte is a substance the dissolves in water to produce a solution that conducts electricity.

  • Ionic substances tend to be electrolytes.

  • Molecular substances tend to be non-electrolytes.


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