Unit 4 Periodic Table and Chemical Change  Introduction to the Atom

Structure of an Atom  A carbon atom consists of protons and neutrons in a nucleus that is surrounded by electrons.

Isotopes  Isotopes are atoms with same number of protons but different number of neutrons.  Examples are C-12 and C-14

Isotopes

Chapter 3 section 2 Organizing Elements  Rows tell us the number of levels of electron an element has.  Rows are called Periods  Elements in columns have similar properties and reactivity  Columns are called Groups or Families  Group # tells # of electrons in outer level

Finding Data on Elements  Each square of the periodic table includes an element’s atomic number, chemical symbol, name, and atomic mass.

Chapter 3 section 2  Organizing the Periodic Table

The Three Major Categories of Elements  Metals  Nonmetals  Metalloids

Metals  elements that are shiny  good conductors of thermal energy and electric current  Malleable (they can be hammered into thin sheets of metal) and  ductile (they can be drawn into thin wires)

Nonmetals  elements that are dull (not shiny)  poor conductors of thermal energy and electric current.  Solid nonmetals – brittle and unmalleable

Metalloids

 or semiconductors, elements that have properties of both metals and nonmetals  Some can be shiny or dull,  some can be malleable and ductile  some can conduct thermal energy and electric current well.

 Most reactive elements are group 1 & 2 on the left side of Periodic Table  Elements decrease in reactivity as they move to the right on Periodic Table.

Forces on Atoms  Gravity – gravitational attraction  Electromagnetic Force – particles with same charge repel, opposite charges attract  Strong Force – force that keeps protons in the nucleus from repelling  Weak Force – effects the unstable atoms, can cause a neutron to change into a proton and an electron

2 types of Chemical Bonds  Ionic Bonds – an unequal sharing of electrons NaCl, H 2 O  Covalent Bonds – equal sharing of electrons O 2, Cl 2

Chemical Equation  Law of Conservation of Mass – states that matter cannot be created or destroyed

Chemical Changes  Chemical change – combustion, electrolysis, oxidation and tarnishing  Signs that chemical change has occurred: Odor, light, heat or sound production, foaming or fizzing and change in color