Atoms and ElementsAtoms and Elements

The Nature of MatterThe Nature of Matter

MatterMatter refers to anything that takes up refers to anything that takes up space and has mass.space and has mass.

Matter is composed of elements, Matter is composed of elements, substances that cannot be broken down substances that cannot be broken down into another substance.into another substance.There are 92 natural elements.There are 92 natural elements.Living organisms are made primarily of six Living organisms are made primarily of six

elements.elements.

The Nature of MatterThe Nature of Matter

The Nature of MatterThe Nature of Matter

Elements:Elements:Made up of tiny particles called Made up of tiny particles called

atomsatomsEach has its own Each has its own

name name atomic number atomic number atomic symbolatomic symbol

Name Number Symbol

Hydrogen 1 H

Aluminum 13 Al

Sodium 11 Na

Atomic StructureAtomic Structure

Atoms have three main sub atomic Atoms have three main sub atomic structuresstructures::

Name Charge Mass LocationName Charge Mass Location

ProtonProton + 1 amu inside nucleus + 1 amu inside nucleus

Electron - 1/1837 amu around nucleusElectron - 1/1837 amu around nucleus

Neutron o 1 amu inside nucleusNeutron o 1 amu inside nucleus

Atomic StructureAtomic Structure

All atoms of the same All atoms of the same element have the same element have the same

number of protonsnumber of protons

It is also equal to the atomic It is also equal to the atomic numbernumber

The Periodic TableThe Periodic Table

The elements are organized to form the The elements are organized to form the periodic tableperiodic table..The columns in the table are groups.The columns in the table are groups.The rows in the table are periods.The rows in the table are periods.

Elements in groups have similar chemical Elements in groups have similar chemical and physical characteristics.and physical characteristics.

The Periodic TableThe Periodic Table

Atomic StructureAtomic Structure

The The Atomic MassAtomic Mass is the number of is the number of

protons plus neutronsprotons plus neutrons

The electrons are so small they are not included in the massThe electrons are so small they are not included in the mass

Atomic Number

N15

7

Mass Number of protons: 7

Number of neutrons: 8

Atomic mass: 15

Review: Finding Atomic PartsReview: Finding Atomic Parts

To find the number of protons –To find the number of protons –Proton # = Atomic number on periodic chartProton # = Atomic number on periodic chart

To find the number of electrons – To find the number of electrons – Electron # = Atomic number on periodic chartElectron # = Atomic number on periodic chart

To find the number of neutrons – To find the number of neutrons – Neutron # = Atomic mass (rounded) Neutron # = Atomic mass (rounded)

minus atomic numberminus atomic number

Review: Finding Atomic PartsReview: Finding Atomic Parts

Atomic Number

Na23

11

Mass

Number of protons: 11 (= atomic #)Number of protons: 11 (= atomic #)

Number of electrons: 11 (= atomic #)Number of electrons: 11 (= atomic #)

Number of neutrons: 12 Number of neutrons: 12

(atomic mass 23 – atomic number 11)(atomic mass 23 – atomic number 11)

Sodium Atomic Particles:

Composition of Matter- ElementsComposition of Matter- Elements

Symbols to know:Symbols to know:

C Carbon Na Sodium Mg Magnesium C Carbon Na Sodium Mg Magnesium

O Oxygen P Phosphorus Fe Iron O Oxygen P Phosphorus Fe Iron

H Hydrogen S SulfurH Hydrogen S Sulfur Ca CalciumCa Calcium

N Nitrogen Cl Chlorine K PotassiumN Nitrogen Cl Chlorine K Potassium

Composition of Matter- ElementsComposition of Matter- Elements

Why are the atomic mass units on the periodic Why are the atomic mass units on the periodic chart not whole numbers?chart not whole numbers?

Some atoms of an element are heavier or Some atoms of an element are heavier or lighter than others – lighter than others –

Atoms of the same element with different Atoms of the same element with different masses are called masses are called ISOTOPESISOTOPES

The atomic mass on the chart is a weighted The atomic mass on the chart is a weighted average of all of the known massesaverage of all of the known masses

Composition of Matter- ElementsComposition of Matter- Elements

IsotopesIsotopesIsotopes have the Isotopes have the same atomic numbersame atomic number

but a but a different atomic massdifferent atomic mass

Atoms of the same element must have the Atoms of the same element must have the same number of protons. same number of protons.

The difference in mass comes from a The difference in mass comes from a different number of neutronsdifferent number of neutrons

Composition of Matter- ElementsComposition of Matter- Elements Isotopes:Isotopes:

Atom #1: 7 protons, 7 neutronsAtom #1: 7 protons, 7 neutronsAtom #2: 7 protons, 8 neutronsAtom #2: 7 protons, 8 neutrons

Not isotopes:Not isotopes:Atom #1: 7 protons, 7 neutronsAtom #1: 7 protons, 7 neutronsAtom #2: 8 protons, 8 neutronsAtom #2: 8 protons, 8 neutrons

Since these two atoms have a different number of protons, Since these two atoms have a different number of protons, they are two different elements, not isotopesthey are two different elements, not isotopes

Composition of Matter- ElementsComposition of Matter- Elements

Isotopes are represented differently, showing Isotopes are represented differently, showing their atomic mass.their atomic mass.

Examples: Examples:

carbon – 14carbon – 14 is an isotope of carbon with a is an isotope of carbon with a mass of 14 (the normal mass is 12) mass of 14 (the normal mass is 12)

iodine – 131iodine – 131 is an isotope of iodine with a is an isotope of iodine with a mass of 131 (the normal mass is 127) mass of 131 (the normal mass is 127)

Composition of Matter- ElementsComposition of Matter- Elements

Radioactive isotopesRadioactive isotopes or radioisotopes: or radioisotopes:

isotopes that are very unstable and isotopes that are very unstable and release energy as they “fall apart” or release energy as they “fall apart” or disintegrate. disintegrate.

This radiation can be detected with a This radiation can be detected with a Geiger counter.Geiger counter.

Uses of Radioactive IsotopesUses of Radioactive Isotopes

Radioactive isotopes can be used as Radioactive isotopes can be used as tracerstracers to follow the movement of that to follow the movement of that element through chemical reactions.element through chemical reactions.

Radioactive isotopes can be used to Radioactive isotopes can be used to sterilize medical and dental instruments.sterilize medical and dental instruments.

Radioactive isotopes can also be used to Radioactive isotopes can also be used to kill cancer cells.kill cancer cells.

Uses of Radioactive IsotopesUses of Radioactive Isotopes

Atomic StructureAtomic Structure Electrons are found in energy levels outside the Electrons are found in energy levels outside the

nucleusnucleus

The first energy level holds two electronsThe first energy level holds two electrons The second energy level holds eight electronsThe second energy level holds eight electrons

The third energy level holds eight electronsThe third energy level holds eight electrons Other levels can hold moreOther levels can hold more

Octet RuleOctet Rule: Stable atoms have eight electrons : Stable atoms have eight electrons in their outer level in their outer level

Arrangements of Electrons in an AtomArrangements of Electrons in an Atom

To Draw an AtomTo Draw an Atom List the number of List the number of

protons, electrons and protons, electrons and protonsprotons

List the number of List the number of electrons to draw in each electrons to draw in each energy level energy level

Write the number of Write the number of protons and neutrons in protons and neutrons in the center (nucleus) of the the center (nucleus) of the atomatom

Draw the electrons on Draw the electrons on circles around the nucleuscircles around the nucleus

Example: SodiumExample: SodiumAtomic # = 11 Atomic mass = 23Atomic # = 11 Atomic mass = 23

P= 11 E = 11 N = 12P= 11 E = 11 N = 12

Electron levels:Electron levels:

First = 2First = 2

Second = 8Second = 8 = 11 = 11

Third = 1Third = 1

P = 11N = 12

Atomic StructureAtomic StructureElectrons in the outermost shell are called Electrons in the outermost shell are called

valence electronsvalence electronsThe valence electrons determine how an The valence electrons determine how an

element will reactelement will reactAll elements in the same column (group) All elements in the same column (group)

of the Periodic table have the same of the Periodic table have the same number of valence electronsnumber of valence electrons

Oxygen has six valence electronsOxygen has six valence electrons