Intro to Chemistry

Periodic Table tidbits Period table organization – organized by

increasing atomic number Split into metals (left side of stair step line)

and nonmetals (right side of stair step line)ONE EXCEPTION

Hydrogen!

vertical columns (#1-18)Groups

horizontal rows (#1-7)Periods

Atomic Structure Nucleus- center of an atom -contains protons

(which are positive) -contains neutrons

(which are neutral)

Ex- Sodium:

Atomic StructureOutside the Nucleus: Electrons (which are negative) surround

the nucleus in energy levels 1st energy level = holds 2e 2nd energy level = holds 8e 3rd energy level = holds 18e 4th energy level = holds 32e

Subatomic Particles Organized

Charge Location Mass

Protons

Neutrons

Electrons

Try it out!Read pp 104-108

then do #3, 4, 5 on page 110

Subatomic Particle Organized

Charge Location Mass

Protons Positive In nucleus 1 amu

Neutrons Neutral In nucleus 1 amu

Electrons Negative Outside of nucleus/ in energy levels

0 amu

Atomic Mass

An atom is defined by the number of PROTONS IT HAS!!!

Chemistry tidbits Chemical Symbol- letter representing the

atom (sometimes from Latin)

Chemistry tidbits Atomic number = number of protons

Don’t kill anyone in my class today! Mass number = # protons + # neutrons

Don’t bother to weigh the air inside the box So how can you calculate NEUTRONS??

Calculating Neutrons is a simple algebraic problem… Atomic Mass = protons + neutrons Atomic Number = protons Write the equation…

Atomic Mass= Atomic Number + neutrons #Neutrons = (mass number – atomic number)

Chemistry tidbits Usually can assume:

OK to round atomic mass to nearest whole number

# protons = # electrons ONLY true for NEUTRAL ATOMS!

And remember…

Don’t mess with the

PROTONS!!!

So what CAN we “mess with?”

Neutrons…Changes the MASSGet an ISOTOPE

Electrons…Changes the CHARGEGet an ION

Atomic Mass Mystery…

Look at the atomic mass for Oxygen. What does it say (exactly?)15.9999

What is the atomic mass?P + N

So what the heck!?!?!Average of the actual isotopes on Earth!!!

Isotopes

Isotopes are different atoms of the same element that contain the same number of protons but different number of neutrons.

Examples Cl-35 vs. Cl-37 17P 17P 18N 20N

How to write isotopes…

Mass/Hyphen Notation: Especially important for a form of the isotope

that is NOT the “usual”Write the symbol, a dash, and the mass # for

that isotopeEx’s

C-14 C-12

How to write isotopes…

Nuclear Symbol Notation Includes the symbol, atomic #, and the mass

# for that isotopeEx’s

14

6C

What else CAN we “mess with?”

Neutrons…Get an ISOTOPE

Electrons…Get an ION

IONS

If you mess with the electrons you change the overall charge of the atom…an atom that is no longer neutral is called an ION.

There will be more on this to come…

How do we Draw Atoms

Bohr Models Lewis Dot Structures

Look at the many things in your classroom or at home: desks, chairs, windows, shoes, etc. If all of these things are made from atoms and all atoms are made of only a few kinds of particles, what accounts for the variety of things that you see?

Atoms of different elements have different atomic numbers. The atomic number tells us the number of protons (+ charge). If the atom is neutral, the number of electrons (-charge) equals the number of protons.

The mass number is the number of protons + the number of neutrons (0 charge). In the following, C-14, the 14 is the mass number. The atomic number for C can be found on the periodic table. C’s atomic number is 6, so it has 6 protons and 6 electrons. To find the neutrons, take the mass number minus the protons (14-6 = 8 neutrons).

In the Bohr Model, the protons and the neutrons are placed in the atomic nucleus while the electrons orbit around the nucleus in stationary levels. Each level can hold only a certain maximum number. The 1st up to 2 electrons, the 2nd up to 8 electrons, the 3rd up to 18 electrons, and the 4th up to 32 electrons.

 

Complete the table below using the information given for each atom.Atom A has 3 protons and 4 neutrons.Atom B has 11 protons and 12 neutrons.Atom C has an atomic number of 19 and a mass number of 39.Atom D has an atomic number of 17 and a mass number of 35.

Atom # of protons

# of neutrons

Atomic # Mass # # of electrons

A

B

C

D

Complete the table below using the information given for each atom.Atom A has 3 protons and 4 neutrons.Atom B has 11 protons and 12 neutrons.Atom C has an atomic number of 19 and a mass number of 39.Atom D has an atomic number of 17 and a mass number of 35.

Atom # of protons # of neutrons

Atomic # Mass # # of electrons

A 3 4 3 7 3B 11 12 11 23 11C 19 20 19 39 19D 17 18 17 35 17

Let’s Draw some Bohr Models!

But…that can be a pain…

Most of the time we only really care about the valence electrons

Valence Electrons- electrons in the outermost shellAlso the GROUP NUMBER!!!

Valence Electrons are what react!

Lewis Dot Structures Lewis dot diagrams- display the

number of valence electrons (outermost electrons) around the element symbol

Used to show how atoms of different elements bond and form compounds

Hint- use group number to find valence electrons

Octet Rule-

Most atoms want to have 8 electrons in their outer shell

How to draw a Lewis Dot Structure1. Find the group # (top of the row on the

PT)

2. Write the symbol.

3. Draw dots around the symbol equal to the group number (if group 2- draw two dots)

1. Place dots one at a time around the top, right, bottom and left side of the atom before you double any up.

How to draw a Lewis Dot Structure1. Find the group # (top of the row on the PT)

Let’s do Phosphorus

2. Write the symbol. P

3. Draw dots around the symbol equal to the group number (if group 2- draw two dots)

1. Place dots one at a time around the top, right, bottom and left side of the atom before you double any up.

EXCEPTIONS!!!

Helium- What is its group number?Why doesn’t it make sense to draw that many

dots? Because it is easier for it to fill that first shell which

only needs two electrons

Electron configurations (Bohr Models)

Lewis Dot Structures