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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
