Chemistry 1

J Young

Matter

• Anything that has Weight and occupies space.

• States of Matter.– Gas– Liquid– Solid

• Density– Mass per unit

volume

The Atom

The Mole

6.02 X 6.02 X 10102323

The Mole

• A counting unit• Similar to a dozen, except instead

of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000

• 6.02 X 1023 (in scientific notation)• This number is named in honor of

Amedeo _________ (1776 – 1856)Amedeo _________ (1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present

How Big is a Mole?

• Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.

• If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

Periodic Table (Symbol)

Mass Number and Isotopes

• Mass number is given the symbol A.• A is the sum of the number of protons and neutrons.• Z = proton number N = neutron number• A = Z + N• • A common symbolism used to show mass and droton

numbers is

Mass Number and Isotopes

• Isotopes are atoms of the same element but with different neutron numbers.• Isotopes have different masses and A values but are the same element.

• One example of an isotopic series is the hydrogen isotopes. • 1H or protium is the most common hydrogen isotope -- one proton and no neutrons • 2H or deuterium is the second most abundant hydrogen isotope -- one proton and one neutron • 3H or tritium is a radioactive hydrogen isotope -- one proton and two neutrons

Chemical Bonding

• Chemical bonding involves sharing of valence electrons between two atoms, because all atoms want 8 atoms in the valence shell, just like the noble gases.

Types of Chemical Bonds

• Covalent bonds – sharing of a pair of electrons.

• Ionic bonds – complete transfer of an electron from one atom to another.

• Metallic bonds – valence electrons are relatively free to move – attracted to multiple nuclei simultaneously; this leads to formation of a sea of electrons.

Ionic Bonding The desired electron shell configuration is

that of noble gases, with a full valence shell.

Ionic bonds result from a transfer of electrons from one species (usually a metal) to another (usually a nonmetal or polyatomic ion). Electronegativity difference of greater than 1.6 or 1.7.Examples: NaCl and MgCl2

Covalent Bonding

• The desired electron shell configuration is that of noble gases, with a full valence shell.

Covalent bonds result from atoms sharing valence electrons Electronegativity difference of less than 1.6 or 1.7.

Symbology of Covalent Bonds (1)

• Chemists often use the symbol "-" to represent a

bond. For example, H-H is a "hydrogen

molecule" and Cl-Cl is a "chlorine molecule." The line in between the two atoms means that they are sharing two electrons between them.

• Pure hydrogen exists as H2 molecules

• Pure chlorine exists as Cl2

• Pure bromine exists as Br2

• Pure iodine exists as I2

Symbology of Covalent Bonds (2)

• Oxygen atoms like to combine to form O2. In this case, each oxygen atom wants 2 more electrons, so when the two oxygen atoms get together they share a total of 4 electrons. We write O2 as:

double bond

Symbology of Covalent Bonds (3)

• Nitrogen likes to combine to form a diatomic molecule, in this case N2. Each nitrogen atom, however, wants 3 electrons, so two nitrogen atoms share a total of 6 electrons.

triple bond

Electronegativity Determines Bonding

• Electronegativity is the tendency of an atom to attract electrons towards itself in a molecule of a compound. The value of electronegativity of an element describes the ability of its atom to com-pete for electrons with the other atom to which it is bonded. Electronegativity is however not the property of an isolated atom.The most widely used scale of electronegativities was devised in the 1930s by Linus Pauling. On the Pauling scale, fluorine, the most electronegative element, is assigned an electronegativity of 4.0 and all other elements are assigned values relative to fluorine.

Electronegativity Trend

Polyatomic Ions & Compounds

Definition -- Element

• consists of only one kind of atom,• cannot be broken down into a simpler type

of matter by either physical or chemical means, and can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).

• A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. Note that the two nitrogen atoms which comprise a nitrogen molecule move as a unit.

Definition -- Compound

• consists of atoms of two or more different elements bound together,

• can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),

• has properties that are different from its component elements, and

• always contains the same ratio of its component atoms.

Definition – Mixture (1)

• consists of two or more different elements and/or compounds physically intermingled,

• can be separated into its components by physical means, and

• often retains many of the properties of its components. Example: fabrics, vinegar, soil, rocks, rocks, milk, lemonade

Definition – Mixture (2)

• Heterogeneous mixtures- the substances in the kind of a mixture are not spread out  evenly. Example: a bottle of liquid salad dressing.

•     Homogeneous mixtures- the substances are spread evenly throughout, a homogeneous mixture is called a solution. Example: vinegar (water and acetic acid are mixed evenly throughout). Other examples: sea water, soft drinks, glass

Definition – Solution

• A solution is a homogeneous mixture in which one substance (the solute) is dissolved in another substance (the solvent). Example: salt water (Water, the solvent, plus salt, the solute, produces the solution of salty water.)

Definition – Suspension

• A suspension is a heterogeneous mixture in which the particles are large enough to be seen by a microscope or the unaided eye (eventually, they settle out of the mixture). Example: stirring a teaspoon of dirt in a glass of water.

Definition – Acid, Base, Salt

acid: generates [H+] in solutionpH < 7base: generates [OH-] in solution pH > 7 salt:acid + base <---> salt + waterexample: HCl + NaOH <---> NaCl + H2O

Acids & Bases can neutralize each other.

THE END