Chapter 11Chapter 11Introduction to AtomsIntroduction to Atoms

• An atomatom is the smallest particle into which an element can be divided and still be the same substance.

• See timeline handout for the development of the model of the atom.

• Identify atom models of Thomson, Rutherford, Bohr, and the Modern Model.

• Know the scientist

• their contribution to the

developing model of an atom

(their experiment)

• their atom model!

What do I need to know?

Structure of the atom

• The atom contains a nucleus surrounded by one or more electrons

• The nucleus contains protons and neutrons.

Draw an atom here

(Page 320)

Structure of the atom

nucleus

energylevel

Particle Charge Location

Particle Charge Location

Proton

Particle Charge Location

Proton Positive

(+)

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron Neutral

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron Neutral Inside nucleus

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron Neutral Inside nucleus

Electron

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron Neutral Inside nucleus

Electron Negative

(-)

Particle Charge Location

Proton Positive

(+)

Inside nucleus

Neutron Neutral Inside nucleus

Electron Negative

(-)

Outside nucleus

Terms to copy in notes:

atomic number – the number of protons in the nucleus of an atom.

(*The number of protons identifies an element!)

atomic mass – the average mass of one atom of an element.

atomic mass unit (amu) – a measurement of the mass of one proton or one neutron.

Chemical Symbols

• A chemical symbol is one or two letter(s) representing an element.

• If the symbol is one letter, it is a printed capital.

Hydrogen symbol is H

• If two letters, the first is a printed capital and second is lower case.

Cobalt symbol is Co

Know the Following Elements!

The first 20 elements and symbols, plus 7 others, must be properly identified together.

iron copper

silver gold

mercury tinlead

• The symbols must be written in correct form.• Spelling counts!

Electrons

• Electrons are located in an electron cloud around the nucleus.

• There are different energy levels (“orbits” in the Bohr model) that electrons fill.

1st energy level can hold 2 electrons2nd can hold 8 electrons3rd can hold 18 electrons4th can hold 32 electrons

Energy Levels of carbon atom

• Today’s periodic table is based on atomic number.

Each element’s square contains: atomic number

(protons)

chemical symbol

element name atomic mass (protons

&

neutrons)

This is an average

26

FeIron

55.847

How to find the number of neutrons in an atom

• Round the atomic mass to the nearest whole number.

• Subtract the number of protons (atomic number).• The difference is the number of neutrons.

boron 10.81 atomic mass (protons + neutrons)

11 rounded - 5 atomic number (protons)

6 neutrons

Aluminum

atomic mass

rounded

- atomic number

neutrons

Practice calculating the number of neutrons in an atom

• Number a blank sheet of paper 1 to 10.

• Write the name for each element from the periodic table for elements 1-10.

• Use the right side of your paper to calculate the number of neutrons for elements 1-10.

• Write your answer next to the elements name.

• Gaining or losing a neutron makes an atom an isotope.

• Isotopes are still the same element, just more or less neutrons.

carbon 12 has 6 neutrons (always 6 protons)

carbon 14

has 8 neutrons (always 6 protons)

The 12 refers to

the mass number

(protons + neutrons)

Valence electrons are electrons farthest away from the nucleus (outer energy level).

- involved with chemical reactions.

- gives an atom its gives an atom its chemicalchemical characteristicscharacteristics..

- can be shared, or transferred.

- Atoms with a full valence energy level are most stable (less reactive).

electron dot diagram – represents the valence electrons of an element.

- uses an element symbol surrounded by dots representing valence electrons.

H O C Ne hydrogen oxygen carbon neon

The Periodic Table of The Periodic Table of ElementsElements

• In 1869 a Russian scientist Dmitri Mendeleev arranged elements in order of increasing atomic mass, and chemical properties.

• He used his table to predict properties of elements not yet discovered!

Chapter 12 Notes

• Today’s periodic table is based on atomic number!

Each element’s square contains: atomic number

(protons)

chemical symbol

element name atomic mass (protons

&

neutrons)

This is an average

26

FeIron

55.847

• An element’s properties can be predicted by its location on the periodic table.

Groups or families:• vertical columns numbered 1-18.• elements have similar properties

Periods:• across rows numbered 1-7• elements have predictably different patterns.

MetalsMetals

• Metals are found to the left of the stair step.• Physical properties:

– Hardness– Shininess (luster)– Malleability (pound into shapes)– Ductility (drawn out into a wire)– Good conductors– Magnetic (Co, Ni, Fe)– Mostly solids at room temp.

MetalsMetals

• Chemical properties:– wide range– Some violently react with water (Na, K)– Some unreactive (Au, Cr)

– Some corrode (react slowly with O2 and flake off)

– Alloys (mixture of metals)• bronze (Cu + Sn)• stainless steel

MetalsMetals

• Elements are increasingly nonmetallic reading left to right.

• Tend to lose electrons forming

positive ions (1+, 2+)

• Alkali Metals– Group 1 (1 valence electron)– Most reactive metals!– Very soft & shiny

MetalsMetals

• Alkaline Earth Metals– Group 2 (2 valence electrons)– Not as reactive as Group 1 but more reactive

than most metals.– Fairly hard, grey-white color– Good conductors of electricity

MetalsMetals

• Transition Metals– Groups 3-12

– Fairly stable, react slowly with H2O

– Similar reactivity between columns– Hard and shiny– Good conductors of electricity

MetalsMetals

• Lanthanides and Actinides– Called rare earth metals– Fit in Periods 6 and 7 between alkaline earth

metals and the transition metals.– Placed below periodic table for convenience.– Soft, malleable, shiny, very conductive

Nonmetals

• Located right of the stair step

• Physical properties:– Most are gases at room temp. (low boiling

point).– dull– brittle– lower densities– poor conductors of heat & electricity

Nonmetals

• Chemical properties:– Most readily form compounds

• Will take electrons from metals forming negative ions (1-, 2-)• Will also share electrons• Many form diatomic molecules (O2, N2, H2)

• Halogen Family– Group 17 (7 valence electrons)– Very reactive!– Dangerous to humans

Nonmetals

• Noble Gases– Group 18– Chemically stable (unreactive)– Do not gain, lose, or share valence electrons

• Hydrogen– Alone in upper left corner– Simplest element– Not grouped in a family

Metalloids

• Along the stair step (7 elements)

• Have some properties of metals & nonmetals

• Used to make semiconductors