What is a chemical change vs. a physical change?

Atoms The basic building block of all matter Consist of: Nucleus Proton (+) Neutrons ( 0 ) Electrons (-)

INSIDE NUCLEUS PROTONS: + CHARGED NEUTRONS: NO CHARGE ALWAYS THE SAME NUMBER OF ELECTRONS TO PROTONS

VALENCE SHELL - IS THE OUTERMOST SHELL

OUTSIDE THE NUCLEUS ELECTRONS: NEGATIVELY CHARGED THEY ARE FOUND IN THE “ORBITAL” OR ENERGY SHELL

Element Made up of atoms CANNOT be broken down Examples: Hydrogen (H), Oxygen (O), Carbon (C), Nitrogen (N)

Elements are found in the Periodic Table

Compound Made up of 2 or more different elements Chemically combined CAN be broken down into its elements EX: H2O

COMPOUND EX: 2 HYDROGEN + OXYGEN = WATER

Put the following in order from smallest to largest Compound, Atom, Element

Molecule A group of atoms held together by covalent bonds and has no overall charge

How to find the number of protons, neutrons and electrons: Atomic number tells you how many electrons or protons are in an element How many protons or electrons are in this element?

how many protons or electrons are in this element? ATOMIC NUMBER ATOMIC MASS

Atomic mass = the number of protons + the number of neutrons To find the number of neutrons, you must subtract the atomic number from the atomic mass

Step 1: Subtract the atomic mass from the atomic number 4 - 2 = 2 2 equals how many neutrons are in this element

How many protons or electrons are in N (Nitrogen) ? How many neutrons are in Nitrogen?

STOP

BOHR MODEL

Bohr Model

Find your element on the periodic table. Bohr Diagrams Find your element on the periodic table. Determine the number of electrons – it is the same as the atomic number. This is how many electrons you will draw.

Find out which period (row) your element is in. Bohr Diagrams Find out which period (row) your element is in. Elements in the 1st period have one energy level. Elements in the 2nd period have two energy levels and so on

The second and third energy levels hold up to 8 electrons each. In the Bohr model of the atom, the first energy level can accept up to 2 electrons. The second and third energy levels hold up to 8 electrons each. The fourth and fifth energy levels hold 18 electrons.

Electrons and energy levels The first energy level can accept up to two electrons. The second energy levels hold up to eight electrons.

Order of Filling in Dots for Electron Dot Diagrams 1 5 4 8 X 2 6 3 7

C Draw a nucleus with the element symbol inside. Bohr Diagrams Draw a nucleus with the element symbol inside. Carbon is in the 2nd period, so it has two energy levels, or shells. Draw the shells around the nucleus. C

C Bohr Diagrams Add the electrons. Carbon has 6 electrons. The first shell can only hold 2 electrons. C

Bohr Diagrams Since you have 2 electrons already drawn, you need to add 4 more. These go in the 2nd shell. Add one at a time -starting on the right side and going counter clock-wise. C

Bohr Diagrams Try the following elements on your own: H He O Al Ne K C

Bohr Diagrams Try the following elements on your own: H He O Al Ne K H

H Bohr Diagrams Try the following elements on your own: H – 1 electron Al Ne K H

He Bohr Diagrams He Try the following elements on your own: H O Al Ne K He

He Bohr Diagrams Try the following elements on your own: H He - 2 electrons O Al Ne K He

Bohr Diagrams Try the following elements on your own: H He O Al Ne K O

O Bohr Diagrams Try the following elements on your own: H He O - 8 electrons Al Ne K O

Al Bohr Diagrams Al Try the following elements on your own: H He O Ne K Al

Al Bohr Diagrams Try the following elements on your own: H He O Al - 13 electrons Ne K Al

Ne Bohr Diagrams Ne Try the following elements on your own: H He O Al K Ne

Ne Bohr Diagrams Try the following elements on your own: H He O Al Ne - 10 electrons K Ne

Bohr Diagrams Try the following elements on your own: H He O Al Ne K K

K Bohr Diagrams Try the following elements on your own: H He O Al Ne K - 19 electrons K

Excited Atoms and Spectral Lines Ground State- when all of the electrons are as close to the nucleus as they can be. Excited State- when at least one electron has jumped to a higher energy level.

Valence Electrons- the electrons in the other shell Group 1 = 1 valence electron Group 2 = 2 valence electrons Group 13 = 3 valence electrons Group 14 = 4 valence electrons Group 15 = 5 valence electrons Group 16 = 6 valence electrons Group 17 = 7 valence electrons Group 18 = 8 valence electrons

STOP

Find your element on the periodic table. Lewis Structures Find your element on the periodic table. Determine the number of valence electrons. This is how many electrons you will draw.

C Write the element symbol. Lewis Structures Write the element symbol. Carbon is in the 4th group, so it has 4 valence electrons. Starting at the right, draw 4 electrons, or dots, clockwise around the element symbol. C

C On your worksheet, try these elements on your own: H P Ca Ar Cl Al Lewis Structures On your worksheet, try these elements on your own: H P Ca Ar Cl Al C

H Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al H

P Lewis Structures On your worksheet, try these elements on your own: Ca Ar Cl Al P

Ca Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ca

Ar Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Ar

Cl Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Cl

Al Lewis Structures On your worksheet, try these elements on your own: P Ca Ar Cl Al Al

Acids and Bases

What is pH? pH Measures how acidic or basic a substance is Acid: has more Hydrogen ions and is represented as a 0 -6.9 on the pH scale. Base: A substance that has LESS Hydrogen ions and more Hydroxide ions is represented as a 7.1 to 14 on the pH scale Neutral: is a 7 on pH scale, and has an equal number of hydrogen and hydroxide ions

pH scale Goes from 0 through 14 Acids are below 6.9 (many foods) Bases are above 7.1 (many household cleaners)

N E U T R A L ACID BASE MOST BASIC MOST ACIDIC

Buffers Weak acids or weak bases pH close to 7 Important to human systems

Important to Humans Cells in the human body have a pH between 6.5 and 7.5. A lower or higher pH will affect the chemical reactions that take place. Natural buffering systems control pH, minimizing harm to cell HOMEOSTASIS