Basic Chemistry Section 2-1

What is an atom?  The basic unit of matter.

What are atoms made of?  3 types of subatomic particles:  Protons  Neutrons  Electrons

The structure of an atom  Atoms consist of a tightly packed nucleus with electrons that orbit it.  Electrons have a negative a negative charge (-).

Electron Configuration  Electrons are found in various shells or clouds that orbit the nucleus  Each shell can hold only a certain number of electrons  1st shell = 2 electrons  2 nd shell = 8 electrons

Valence electrons  The electrons found in the outermost shell are called valence electrons

What’s in the nucleus?  The nucleus holds the protons and neutrons.  Protons are positively charged (+)  Neutrons are neutral (0)

The charge of an atom  In an atom, there are an equal number of protons (+) and electrons (-).  Therefore, atoms are balanced and have no overall charge.

Element  A chemical substance that’s made of only one type of atom.  There are over 100 types  i.e. pure gold, carbon, hydrogen, etc.

6 Essential Elements for Life  There are 6 elements that are required for living organisms  Carbon (C)  Hydrogen (H)  Oxygen (O)  Nitrogen (N)  Phosphorus (P)  Sulfur (S)

Periodic Table of Elements  A chart that is used to organize elements based on their atomic number.

Atomic number (Z)  Shows the number of protons in each atom  Each element has its own unique atomic number.  Ex:79 protons = Gold 6 protons = Carbon 6 protons = Carbon

Reading the periodic table  Atomic number (Z)  Chemical symbol  Atomic mass (A)

Chemical Symbols  Each element has a one or two letter symbol.  The first letter MUST be capitalized.  The second letter (when present) must be lowercase.

Atomic Mass (A)  Shows the average mass of the atom  Measured in a.m.u. (atomic mass units)  Each proton weighs one a.m.u.  Each neutron weighs one a.m.u.  Electrons are so small they do not affect the mass

 In other words, the atomic mass tells us how many protons and neutrons are in the nucleus.  #of Neutrons = Atomic Mass (A) - #of Protons

Chemical Bonds

 There are 4 major types of bonds.  Hold atoms together to form molecules  Store energy  Involve valence electrons

Compound  A substance formed by the chemical combination of two or more elements.  Ex:  H 2 O – water  NaCl - Salt

1) Van der Waals Force (Extremely weak)  Created when normal movement of electrons causes temporary charges and attraction.

2) Hydrogen Bond (Weak)  Formed between hydrogen and certain other atoms  Most commonly oxygen, nitrogen and fluorine

3) Ionic Bond (Medium)  Created when one atom “steals” an electron from another atom, thus creating ions (one positive, one negative).  The attraction between these oppositely charged ions forms the bond

4) Covalent Bond (Very Strong)  Created when atoms share electrons.

All bonds store chemical energy!

What is a compound?  Any combination of two or more elements in definite proportions.  Ex: Every water molecule is made of two hydrogen atoms and one oxygen atom. H2OH2OH2OH2O

What is pH?   It tells us if a chemical is an acid, base, or neutral   Based on a scale from 0 to 14

Acid   Any chemical with a pH below 7   Releases hydrogen (H+) ions in water

Base   Any chemical with a pH above 7   Releases hydroxide (OH-) ions in water

Neutral   Any chemical with a pH of exactly 7   Neither an acid nor a base   Ex: Water

Buffer   A chemical that keeps the pH from changing significantly.