Transcript Materials Section B Power point

Periodic Trends
MATERIALS PART B
History
 Mendeleev-Russian 1869
 organized elements
according to mass and
properties
 noticed that properties
repeated periodically
 predicted elements, later
identified as Sc,Ga,Ge
History
 Henry Moseley-1911
 Used X-rays for determining the # of protons
 This is how our current periodic table is arranged.
Periodic Law
 Physical and chemical properties repeat periodically
if arranged according to atomic number.

“Recurring or reappearing from time to time;”
http://www.thefreedictionary.com
 Look for patterns
History
 Additional changes since Medeleev
 Noble gases- William Ramsay (1906)
 Lanthanides/Actinides- Glenn Seaborg (1950)
The Electrical Nature of Matter

Protons- positive
mass of 1 atomic mass unit
(amu)
 in nucleus


Electrons- negative
very small mass
 outside of nucleus


Neutrons-neutral (no charge)
mass 1 amu
 in nucleus

The Electrical Nature of Matter
 Let’s try
 An atom has:
15 protons + 15 electrons =
 20 protons + 21 electrons =
 19 protons + 18 electrons =
 10 protons + 12 electrons=

Counting Subatomic Particles
 Atomic Number
 # of protons
 Identifies the element

- this also equals the # of electrons because atoms are neutral
Counting Subatomic Particles
 Mass Number
 # of protons + # of neutrons
 Find this by rounding the mass on the periodic table

Examples: See practice sheet
Ions and Ionic Compounds
 Ions:
 charged atoms;
 atoms that have gained or lost electrons to form negative or
positive ions
 Ionic Compounds: compounds composed of positive
and negative ions
The Electrical Nature of Matter
 Opposites attract this is the glue to hold atoms together
 These are chemical bonds.
Ions and Ionic Compounds
 Cation: a positively charged ion (Na+)
 Anion: a negatively charged ion (Cl-)
 Polyatomic ion: (many-atoms) an ions made of two
or more bonded atoms (NH4+ or NO3-)
Ions and Ionic Compounds
 Step 1: Write the symbols for the ions side by side, with
the positive ion (or most metallic element) first
 Step 2: Cross over the charge values to give subscripts
 Step 3: Check the subscripts by making sure the total
charge of ions in the compound is zero, simplify
 Step 4: Write the formula
Ions and Ionic Compounds
 Let’s try: Need to use ion chart
 zinc oxide
 aluminum sulfide
 calcium carbonate
Ions and Ionic Compounds
 Naming Compounds
 Nomenclature: the method of naming chemical compounds
1. write the name of the element having a positive
charge
2. add the name of the negative element
3. the negative element must be modified to end in –
ide
Ions and Ionic Compounds
 Let’s try: Use the chart of ions
 NaI2
 K2O
 BaSO4