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6.1 Elements Combine to from Compounds
Compounds form when two or more different atoms combine.
Properties of compounds depend on which atoms are in the compound and how the atoms are arranged.
Properties of compounds are different than that of just elements that make them up.Ex) Water is made out of Hydrogen and Oxygen, and H
and O are both colorless gas at room temperature. But when these two elements make a compound, they are liquid at room temperature.
Compounds always contain atoms with a specific ratio.Ex) Ammonia (NH3)has a 3:1 (3 to 1) ratio of
hydrogen to nitrogenIf this ratio was different, we would not have
ammonia anymore. For example if we had a 1:3 ratio of hydrogen to nitrogen we would not have a compound called Hydrazoic Acid (HN3).
Ammonia (NH3)Hydrazoic Acid (HN3)
Chemical formulas like that for ammonia, NH3, uses the chemical symbols for the element to represent the atoms in a compound.Ex) Carbon dioxide has one carbon and two
oxygens in it.Step 1: Find the chemical symbols for the elements
Carbon—C Oxygen—O Write these side by side–CO
Step 2: To show that there are two oxygens, you must write a “2” by it on the right in a subscript.
Step 3: Now you have your compound—CO2
Counting Atoms
Directions:
1. Write down the different elements in each compound.
2. Write down how many of that particular atom there are
3. How many atoms are there total in the compound.
2 H2SO4 2 Mg(SO)4
1) CH4 2) 4 HNO3
3) 4 Mg(OH)2 4) MgCl2
5) 4 Li2O 6) (NH4)3PO4
1. Atoms bond because they want to be ________________.
2. Atoms are _____________ when they have ___ electrons in the outer shell. (Octet Rule)
3. In order to get ___ electrons in the outer shell, atoms _________, _________ or__________ electrons with/from other atoms.
4. The 18th Group, the _______________are already stable.
Stable
Stable
88
sharetakegive
Bonding and Valence Electrons
Noble Gases
Valence Electrons
Electrons in the outer shell are called _________________electrons
____________________ are the electrons responsible for bonding two atoms together
Noble gases are stable because they have ____ valence electrons; all other atoms want the stability that noble gases have
valence
Valence electrons
8
The number of Valence electrons can be determined by the number of the ___________
Group #1 has ____ valence electron; Group #2 has ____ valence electrons;
Group #17 has ____ valence electrons
Valence Electrons (Continued)
Chlorine—Halogen Sodium—Alkali Metal
group
12
7
Ionic Bonding NotesIons are formed when atoms ______________ or
____________ electrons___________ electrons makes a positive ion___________ electrons makes a negative ion
Metals lose electrons to have ___ electrons in their outer shellNonmetals ______ electrons to have 8 electrons in their outer
shell.
gain lose
Losing
Gaining
8
gain
Ionic Bonding
Ionic bonds form when there is an attraction between positive and negative ions.
We know that the Alkali Metals like to form positive ions (lose e-), and the Halogens like to form negative ions (gain e-).
This means that if Sodium (Na) loses an electron, Chlorine (Cl) will pick it up. We now have a sodium ion (Na+) and a chloride ion (Cl-).
These opposite charges will attract one another and they will bond and this is called an ionic bond.
Ionic Bonding (Continued)
Chlorine
Chlorine, a nonmetal, makes a negative ion
Sodium
Sodium, a metal, makes a positive ion
OPPOSITES ATTRACT
Naming Ionic CompoundsThe name for the positive ion stays the same from the
atom from which it was formed.The name for the negative ion is formed by dropping the
last part of its name and adding the suffix “–ide” to it.To complete the name of the compound put the positive
ion first followed by the negative ion.Ex) Table salt
Na+ and Cl- come together to form NaClNa+ is now “sodium”Cl- was chlorine, but since it is the negative ion it
changes to “chloride”Result: sodium chloride
Covalent BondsA __________is a pair of shared electrons
between two atoms that are________.When forming covalent bonds, neither
atom ______or _____ electrons, so no ion is formed.
Covalent bonds are often represented by a line between two atoms. Most common is the ball-and-stick model.
covalent bond
nonmetals
gains loses
Covalent Bonds (cont.)The number of covalent bonds that an atom
can make depends on the number of ____________that it has.Ex) The Halogens (Group 17) and Hydrogen only
have ___valence electrons. This means that they can only form one covalent bond.
Ex) The atoms in Group 16 have ___ valence electrons. This means that they can from two covalent bonds.Remember that all atoms want to be stable and have
____valence electrons.Ex) The atoms in Group 15 ( 5 valence e-) can form
______covalent bonds.Ex) The atoms in Group 14 (4 valence e-) can from
______ covalent bonds.
Valence electrons
7
6
8
three
four
Covalent Bonds (cont.)Ex) Methane, CH4, can form _____
covalent bonds because carbon has ____ valence electrons. These are all single bonds because carbon is sharing only _____ pair of electrons with each hydrogen.
four
four
one
Double BondsWhen atoms share more than one pair of
valence electrons, a _________can from.A double bond forms when ________ of
valence electrons are shared.Ex) The carbon atom in carbon dioxide,
CO2, forms double bonds with each _________ atom.
double bond
two pairs
oxygen
Triple BondsA triple bond forms when an atoms share
____ pairs of valence electrons.Ex) Two nitrogen atoms can because they
have 5 valence electrons each atom, and they want 8.Because they want to get to 8, they each share
3 valence electrons. This results in the two nitrogen atoms sharing ____electrons, or three pairs.
N N
three
6
A group of atoms held together by covalent bonds is called a________.
Molecules can have anywhere from two to _________of atoms in them.
Some molecules have only atoms of one element.These are called _______molecules.H2, N2, O2, F2, Cl2, Br2, and I2
molecule
thousands
diatomic
Polar Covalent BondsIn a iodine (I2) molecule, both atoms are the
same and the shared electrons are attracted equally to both nuclei.
If the two atoms involved in a covalent bond are __________then some electrons will be attracted to one nucleus more than the other.
A covalent bond in which the electrons are shared unequally is called a ______________. Remember that “polar” means that something has
to extremes, like a magnet with to opposite poles.
very different
Polar covalent bond
Polar Covalent Bonds (cont.)In a water molecule (H2O), the oxygen atom
attracts electrons more strongly than hydrogen atoms do. Because oxygen has eight protons in its nucleus
and the hydrogen only has one proton, the oxygen pulls electrons stronger towards it. This means that the oxygen side has a slightly negative charge and the hydrogen side has a slightly positive charge.
Ionic Compounds
Most ionic compounds have a regular crystal structure.
Their structures depend on the ratio of their atoms and the sizes of the ions that make them up.
Covalent CompoundsUnlike ionic compounds, _______ compounds can
exist as individual molecules.Chemical bonds give each molecule a specific,
three-dimensional shape called its ________ structure.
Molecular structure can influence how a ________ interacts with other substances.
Molecular structure can also affect how we detect them or how our bodies respond to them.Molecules with certain shapes will fit into certain
receptors in our nose that we can smell.Some drugs work while other don’t because specific
receptors in the body only allow certain shapes to fit.
covalent
molecular
molecule
Lewis Dot StructuresThese depend on the number of valence
electrons. These are the outer-most electrons.
polar covalentbond
ionic bond