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 Structure Outside the Nucleus: Electrons (which are negative) surround the nucleus in energy levels 1 st energy level = holds 2e 2 nd energy level = holds 8e 3 rd energy level = SAVE 4 th energy level = FOR CHEMISTRY!!

Subatomic Particles Organized ChargeLocationMass Protons Neutrons Electrons

Try it out! Read pp then do #3, 4, 5 on page 110

Subatomic Particle Organized ChargeLocationMass ProtonsPositiveIn nucleus1 amu NeutronsNeutralIn nucleus1 amu ElectronsNegative 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 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… Mass Number = protons + neutrons Atomic Number = protons Write the equation… Mass Number= Atomic Number + neutrons #Neutrons = (mass number – atomic number)

Chemistry tidbits Usually can assume:  # protons = # electrons ONLY true for NEUTRAL ATOMS!

And remember… Don’t mess with the PROTONS!!!

So what CAN we “mess with?” Neutrons…  Changes the MASS  Get an ISOTOPE Electrons…  Changes the CHARGE  Get an ION

Atomic Mass Mystery… Look at the atomic mass for Oxygen. What does it say (exactly?)  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 isotope  Ex’s C-14 C-12

How to write isotopes… Nuclear Symbol Notation  Includes the symbol, atomic #, and the mass # for that isotope  Ex’s 14 6 C

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. WE WILL LEARN ABOUT IONS LATER WHEN WE DO BONDING!!

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 1 st up to 2 electrons, the 2 nd up to 8 electrons, and the 3 rd, 4 th, etc. hold even more 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 B C D

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 shell  Also 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 Structure 1. 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 Structure 1. 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