The Composition of Chemical Compounds

Dr. Jared Heidinger M.D. Ph.D

•When neutral atoms collide, an electron is transferred from one atom to the other

•Ions – particles that have an electrical charge due to a transfer of electrons

•Monoatomic ions – single atoms that have lost or gained electrons

•high reactivity due to unfilled or overfilled electron levels

•Cations - + charged ions (metals, formed when they lose an electron)

•Anions – neg. charged ions (non-metals, formed when they gain an electron have -ide ending)

•When an atom loses an electron its charge changes from neutral to positive

•eg. Na - 1 electron = Na+

•The Na atom now has 11 protons and 10 electrons.

•The sodium atom now has a net positive charge.

•When an atom gains an electron its charge changes from neutral to negative

•eg. Cl + 1 electron = Cl-

•The Chlorine atom now has 17 protons and 18 electrons. It has a net neg. charge

•Atoms or groups of atoms with a net(overall) negative or positive charge are called ions.

•ASSIGN – pg. 68 - #’s 14, 17, 18

•“10-2” Worksheet and “Atomic Structure” side two - Ions

•Compounds contain two or more elements

•Evidence - electrolysis (electro = electrical; lysis = loosen)

•Large scale electrolytic cells are used to produce separate water into oxygen and hydrogen gas which can then be used in industry

•Industries use this quality for electroplating cars(chrome)

•Remember: phys. And chem. charac. Of elements relate directly to the number of protons and electrons its atom contains.

Two types of ions:•Monoatomic ions(simple ions) - form from the atoms of an element

•eg. Cl forms Cl-

•Polyatomic ions(complex ions) - PO4

3-

ionic compounds•In a chem. Rxn. The #’s of protons and neutrons do not change.

•Valence electrons are involved in chemical reactions

•for elements to join and become compounds, they must form chemical bonds

•chemical bonds: bonds resulting from the forces of attraction between atoms

•Ions are attracted to nearby ions of opposite charge.

•The force that holds any two oppositely charge ions together is an ionic bond.

•In a substance many of these attractions make it possible for the compound to stay together.

•This interaction between - and + charges gives stability to the substance

•This explains why ionic compounds are solids at room temperature

Formation of a Compound

•When a compound is formed, the sum of the charges must be zero

•eg) 1 negative charge + 1 positive charge = zero

•so...

•eg) When aluminium is in its ionic form it has a charge of (3+)

•When chlorine is in its ionic form it has a charge of (1-)

•When aluminum and chlorine form an ionic compound the formula is AlCl3

•It is like this because you need 3 chlorine molecules with a (1-) charge to even out the 3+ charge aluminum has.

Another example...

•Na+ + Cl- ---> NaCl•The ion number tells us how many electrons will be lost or gained by the element.(ion number found on periodic table)

•the overall charge of the product must be zero

• so if one Na ion has a charge of 1+ in order for it to join the chlorine ion it needs to be balanced by a charge of negative one.

•Since one chlorine ion has a charge of negative one only one is needed. Unlike the previous example where 3 chlorine atoms were needed.

•The strength of an ionic bond varies, depending upon the kinds of atoms involved.

•All ionic compounds share these similar characteristics...

ionic compounds: Characteristics

•metallic and non-metallic elements

•ionic bonding(transfer of electrons)

•solutions conduct electricity•solid at room temperature

Solubility•If a compound has high solubility it will dissolve in water.

•If it is insoluble the compound will form a precipitate(visible pieces of matter, cloudiness in the solution)

•Highly soluble ionic compounds can be separated by using a precipitating agent such as alum, to make the soluble compounds removable.

Assignment•“Chemistry: Practice Writing formulas” worksheet

•“Review of Chapter 2: periodicity, atoms, Ions” Worksheet

•“Ions” workSheet (teach how to use key)

Covalent Compounds

•Non-metal to non-metal•electrons not transferred, they are shared

•both atoms attract the electrons, the electrons can’t move to either atom, they find a position in the middle

•The bond that forms when electrons are shared is called a covalent bond.

•Substances that are formed in this way are called covalent compounds.

•Attraction not as strong as an ionic bond.

•For this reason, compounds that are made by covalent bonding, are also called molecular compounds

•Molecular compounds are generally softer than ionic compounds and exist as gases, liquids, or solids at room temperature.

Molecular compounds: characteristics

•Usually formed from non-metallic elements only

•covalent bonding (shared electrons, tug-of-war)

•solutions will not usually conduct electricity

•solid, liquid, gas at room temp.

Diatomic and Polyatomic elements

•some molecular elements are diatomic and some are polyatomic in their natural form

•H2, N2, O2, F2, Cl2, Br2, I2,P4, S8

(Highlight and memorize!!!)

Naming Compounds•IUPAC (International Union of Pure and Applied Chemistry)

•makes rules and guidelines for all aspects of the study of chemistry

•Handout - Chemical Nomenclature

Rules for Naming Binary Ionic Compounds(two

elements)•includes both elements in the compound

•metallic element name appears first.

•non-metallic element appears last, and its ending is changed to -ide.

Rules continued...

•name does not show the charge of the elements in the compound

•name is not capitalized, lower case letters are used.

• Some compounds have common names (eg. - water) Become familiar with the systematic and common name.

Multi-valent ions•some transition metals have two possible charges

•eg. Cu has two different ion forms, Cu+ and Cu2+

•this is a multi-valent ion•you must know what charge is being used

•The formation of copper(I)chloride looks like this:

•Cu++Cl- ---> CuCl•one positive charge is neutralized by one negative charge

•The formation of copper(II)chloride looks like this:

•Cu2++Cl- ---> CuCl2•The copper ion has two positive

charges. •This indicates that there need to be

two negative charges added to neutralize it.

How do you write the word formula with multivalent

compounds?•You must indicate the charge that is being used with roman numerals

•CuCl2 - copper(II)chloride

•Fe2O3 - iron(III)oxide

•“Ionic Naming Practice”•Ionic and Molecular Naming Worksheet

Acids•Acid - aqueous hydrogen compound that makes blue litmus paper turn red

•ph of less than 7•hydrogen written first most of the time, unless it comes at the end of a COO- group, like CH3COOH(aq)

Naming Acids

•refer to chart on the periodic table you received

•start by naming the compound as an ionic compound, then check to see if there is an (aq), if there is it is an acid

•H2SO4(aq) - hydrogen sulphate --> sulphuric acid

•CH3COOH(aq) - hydrogen acetate --> acetic acid

Bases

•all aqueous solutions of ionic hydroxides (anything dissolved in water that has a hydroxide ion attached) make red litmus turn blue

•ph more than 7

Naming Bases•the name of the base is the same as the name of the ionic name

•NaOH(aq) - aqueous sodium hydroxide

•Ba(OH)2(aq) - aqueous barium hydroxide