Chemical Bonding

Electron Cloud Electrons are located around the nucleus in the electron cloud. The cloud is arranged into levels called shells or energy levels. The elements in a period have the same number of levels or shells. 1st Period = 1 Shell 2nd Period = 2 Shells 3rd Period = 3 Shells 4th Period = 4 Shells

Electrons Remember from Chapter 4- each column is called a group. Each element in a group has the same number of electrons in their outer orbital, or “shell”. Each shell can hold a specific number of electrons 1st= 2 electrons 2nd= 8 electrons 3rd= 8 electrons A shell must be filled before moving to the next level The electrons in the outer shell are called “valence electrons”

Turn to your periodic table and label… Group 8 = 8 electrons Group 1 = 1 electron Except for He, it has 2 electrons Group 2 = 2 electrons 3 4 5 7 6

Determine the number of shells and the number of valence electrons to create Bohr Diagram for: Carbon - C 2nd Period = 2 shells 4th Group = 4 valence electrons www.chem4kids.com

Now you try: Ne Name the element. Number of shells ? Valence electrons ? Neon 2nd Period = 2 shells 8th Group = 8 valence electrons

Be Try another: Name the element. Number of shells ? Valence electrons ? Beryllium 2nd Period = 2 shells 2nd Group = 2 valence electrons

S Last one: Name the element. Number of shells ? Valence electrons ? Sulfur 3rd Period = 3 shells 6th Group = 6 valence electrons

Electron Dot Diagrams & Chemical Bonding

The goal of an atom The goal of an atom is to be “happy.” An atom is happy when it has a full outer energy level

How many valence electrons does this need to be “happy?” A. B.

How many valence electrons does this need to be “happy?” C. D.

How many valence electrons does this need to be “happy?” E. F.

How to draw Electron Dot Diagram Step 1: Write down Element symbol Step 2: Find out how many valence electrons there are Step 3: Place electrons around the symbol one at a time and if there is enough double up O= 6 ValenceElectrons

Some common Examples Sodium Na 1 valence electron 2. Argon Ar 8 valence electrons

Practice Problems Use your periodic table to find the number of valence electrons for each of the following. Then, draw an Electron Dot Diagram for each. Carbon Lithium Krypton Boron Neon Nitrogen Flourine Helium Aluminum Calcium

Chemical Bonding Chemical Bonding- combining of atoms to form molecules or ionic compounds Chemical Bond- what holds the atoms together

Periodic Table Remember from last week, the periodic table tells you how many valence electrons an atom has. If we know the number of valence electrons, we can figure out which atoms combine and how.

Noble Gases All have 8 valence electrons except Helium which has 2 All of these atoms are happy because their outer shell is full. Since they are happy, they are not likely to form compounds.

Three types of Bonding Ionic- between metal/nonmetal Covalent- between nonmetals Metallic- between metals

Ionic Bonding Ionic Bonding- bond that forms when electrons are transferred from one atom to another Ions- charged particles that form when an atom gains or loses electrons This occurs between a metal and a nonmetal Polyatomic ion- ionic bond with more than one bond NaOH and NO3

These are both the same element. How? A B. What is the element for A? How many valence electrons are missing from A to make it happy? Is it easier to gain 5 electrons or lose 3 electrons? What is the name for B?

Gain or Lose If you lose electrons, the charge becomes a positive If you gain electrons, the charge becomes a negative

What bonds with what? Positive charges bond with negative charges Positive always is written first You may have to increase the number of atoms to balance the bond

Cheat

Ionic Bonding Steps Using 2 different colors, draw the electron dot diagram for each atom Decide whether each will gain or lose electrons Draw arrows to show where the electrons are transferred Write in the new charge for each molecule

Ionic Bonding Bond Sodium(Na) with Fluorine(F). Bond Beryllium(Be) with Oxygen(O). Bond Aluminum(Al) with Phosphorus(P). Bond Magnesium(Mg) with Sulfur(S).

Cross Bonding Good when charges are not equal Bond Aluminum with sulfur Top number loses charge and goes to bottom number Al+3 S-2 Al2 S3 Answer=Al2S3

Now try cross bonding yourself Bond Fluorine with Boron Bond Aluminum with Selenium Bond Chlorine with Gallium Bond Silicon with Sulfur.

Covalent Bonds Covalent bond- formed when atoms share one or more pairs of electrons these form molecules Shared Electrons H H

2 different types of covalent bonds Polar bonds- electrons are shared unequally Nonpolar bonds- electrons are shared equally

Covalent Bond H2O

Steps for Covalent Bonding Draw the EDD for all elements Look for ways to make the “puzzle pieces” fit together If two elements are sharing an electron it will be on the same side

Water is made of covalent bonds

Charge vs. Number B+3O-2 B2O3 charge TOP how many BOTTOM

Now try drawing some on your own! NH3 H2S CH4 Cl2 CO2

Metallic Bond Metallic bond- attraction between a positive metal ion and the electrons surrounding it Alloy- has two or more metals that are bonding together

Alloy Properties Resist rust Ductile-put into a wire Malleable- flattened into sheets

Properties of Covalent bonds Low melting points Poor conductivity Do not break up into ions

Properties of Ionic Forms ionic crystals Has high melting points Bonds are broken by electricity

Make the following molecules using puzzle pieces: CO2 C2H4 F2 C2H6 Cl2 H2O O2 C2H2 N2 Br2 I2 NH3 PCl3 CH4 SiO2