Transcript Chapter 17 - Mrs. Wiedeman

Chapter 17
Properties of Atoms and
the Periodic Table
Section 1 – Structure of the Atom

Look at elements and their symbols
What’s in an atom?
Atom: smallest piece of matter that still
is the element
 Nucleus: positively charged center of
atom containing

– Protons: particle with 1+ charge
– Neutrons: particle with NO charge

Electrons: surround nucleus in cloud
and have 1- charge
Even smaller…
Quarks: make up protons and neutrons
NOT electrons
 Found using a particle accelerator

– Speed up particles and smash them into
each other
– Found 6 quarks
Models
Represent things that are hard to
visualize
 Model of the atom has changed many
times
 Pg. 510 in book

Today’s model of atom

Electron cloud model: nucleus in
middle and cloud around nucleus where
electrons are most likely found
Section 2 – Masses of Atoms

Nucleus has most of mass
– Proton: 1.6726 x 10-24 g
– Neutron: 1.6749 x 10-24 g
– Electron: 9.1093 x 10-28 g

Mass of proton and neutron are about
2,000 times bigger than electron!!
Atomic Mass
Need better numbers for masses
 Atomic Mass Unit (amu)
 Proton: 1 amu
 Neutron: 1 amu
 Electron ~ negligible

Protons Identify Element
Each element has different # of protons
 The number of protons tells you what
type of element you have
 Atomic Number: the number of protons

Mass Number
Mass Number: SUM of protons and
neutrons
 # of neutrons = mass # - atomic #
 Carbon – 12 and Carbon – 14

Mass Number
Mass Number
How many neutrons are in the Carbon14 atom?
 Sodium has a mass number of 23. How
many protons and neutrons does it
have?
 Copper – 63: how many protons and
neutrons?

Isotopes
Def: atoms of the same element that
have different # of neutrons
 Isotopes: Boron – 10 and Boron – 11
 Average Atomic Mass: weightedaverage mass of mixture of isotopes

Calculating Average Atomic
Mass

Four out of five boron atoms are boron11 and one out of five are boron-10.
What is the AAM?
Section 3
The Periodic Table
Organizing the Elements
Periodic – repeated in a pattern
 Late 1800s – Dimitri Mendeleev –
Russian – organized elements by
increasing masses
 Discovered a pattern with chemical
properties, they repeated  Periodic

Mendeleev’s Periodic Table
Current Periodic Table

1913 – Henry Moseley – English –
organized elements by increasing
atomic number
The Atom and the Periodic Table
Vertical columns = Groups / Families
 Use A group numbering
 Families have similar properties

Location of Electrons
In neutral atom, # of protons = # of
electrons
 Energy levels

– close to nucleus = low energy
– farther away = higher energy
Energy Levels and Electrons
Same group = same # of e- in outer
energy level
 Energy levels are 1 – 7
 Filled outer energy level = 8 e Levels 3 and higher have inner sublevels

Energy Levels and Electrons
Horizontal rows = Periods
 Increase by 1 p+ and 1 e- as you move
right
 Each row ends with atom with filled
outer energy level

Electron Dot Diagrams
Group #s = # valence e-s (outer e-s)
 Def: uses the element symbol and dots
to represent outermost electrons
 Atoms bond to get a filled outer energy
level
 Which groups would likely react?

Regions of the
Periodic Table
Metals, Non-metals, and
Metalloids
Metals

Conductors of heat and electricity
 Luster/shine
 Mostly solid
Nonmetals

Poor conductors of heat and electricity
 Many are gases
 Solids are brittle
Metalloids
• Semiconductors
of
heat and electricity