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 Carbon-14 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: weighted-

average mass of mixture of isotopes

Calculating Average Atomic Mass Four out of five boron atoms are boron-

11 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 sub-levels

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