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 (NH 3 )has a 3:1 (3 to 1) ratio of hydrogen to nitrogen If 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 (HN 3 ). Ammonia (NH 3 ) Hydrazoic Acid (HN 3 )

Chemical formulas like that for ammonia, NH 3, 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—CO 2

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 H 2 SO 4 2 Mg(SO) 4

1) CH 4 2) 4 HNO 3 3) 4 Mg(OH) 2 4) MgCl 2 5) 4 Li 2 O 6) (NH 4 ) 3 PO4

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 18 th Group, the _______________are already stable. Stable 8 8 share take give 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—HalogenSodium—Alkali Metal group 1 2 7

Ionic Bonding Notes Ions 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 shell Nonmetals ______ electrons to have 8 electrons in their outer shell. gainlose 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 Compounds The 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 NaCl Na + is now “sodium” Cl - was chlorine, but since it is the negative ion it changes to “chloride” Result: sodium chloride

Covalent Bonds A __________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 gainsloses

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 three four

Covalent Bonds (cont.) Ex) Methane, CH 4, 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 one

Double Bonds When 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, CO 2, forms double bonds with each _________ atom. double bond two pairs oxygen

Triple Bonds A 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. NN 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.  H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 molecule thousands diatomic

Polar Covalent Bonds In a iodine (I 2 ) 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 (H 2 O), 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 Compounds Unlike 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 Structures  These depend on the number of valence electrons. These are the outer-most electrons.

polar covalent bond ionic bond