Atoms and Elements

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Atoms and Elements

• What is everything in the universe made of?

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What do you remember from 7th grade?

• The periodic table shows approximately 120 known
  elements
• Elements can be classified as metals, nonmetals,
  and metalloids
• When two or more elements combine, they form a
  compound

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What are the elements made of?

• Element-the simplest pure substance.
• Elements are made of atoms, and each elements
  atoms are unique to that element
• Atoms-the basic building blocks of all matter.
  They are the smallest particles into which an
  element can be divided and still be the same
  substance.
• Atoms are made of 3 types of particles-protons,
  neutrons and electrons

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ELEMENTS

• Are atoms
• Identified by its atomic ( of protons)
• Arrangement of electrons determines the elements
  properties such as conductivity and reactivity.

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Overview
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Groups/Families

• Columns of the periodic table that consist of
  elements that have the same number of valence
  electrons.
• Groups 1 and 2 - same as group
• Groups 13-18 - 10 - the group
• Groups 3-12 - no general rule.

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Periods

• Rows of the periodic table that consist of
  elements with the same number of electron clouds
  or energy levels.

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Alkali Metals

• Group 1
• All metals
• 1 Valence Electron
• Very reactive
• Li, Na, K, Rb, Cs, Fr

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Alkaline-Earth Metals

• Group 2
• All Metals
• 2 Valence Electrons
• Very reactive but less than group 1.

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Transition Metals

• Groups 3-12
• All metals
• 1-2 valence electrons
• Less reactive than group 2
• Also contain lanthanide and actinide series
  (radioactive/unstable).

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Groups 13-16

• Elements change from metals to nonmetals and
  include the metalloids.
• Atoms have 10 fewer valence electrons than the
  group .
• Boron Group 13 - 3 valence electrons
• Carbon Group 14 - 4 valence electrons
• Nitrogen Group 15 - 5 valence electrons
• Oxygen Group 16 - 6 valence electrons

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Halogens

• Group 17
• All nonmetals
• 7 valence electrons
• Very reactive
• Only need to gain 1 more electron.

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Noble Gases

• Group 18
• All nonmetals
• 8 valence electrons - except helium only has 2.
• Unreactive
• Have a full outer electron cloud (energy level).

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Hydrogen stands alone

• 1 valence electron
• Very reactive
• Reacts violently with Oxygen under the right
  conditions.

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The Structure of an Atom

• Protons positively charged particles inside the
  nucleus (center).
• Neutrons neutral particles inside the nucleus
  that have No charge.
• Electrons negatively charged particles in atoms
  found around the nucleus.

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Atomic Particles
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The History of Atomic Theory
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Democritus 440 BCE

• Greek Philosopher 2445 years ago.
• Called particles that made up stuff ATOMS
• Atomos (Greek word)
• not able to be divided(uncuttable)
• small hard particles
• Constantly move

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Dalton - 1803

• Atoms make up all substances (the elements)
• Atoms can not be created, divided or destroyed.
• Atoms combine to make other substances.
• Conducted experiments

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J.J. Thomson - 1897

• Discoverd negatively charged particles in atoms
  called Electrons.
• Conducted Cathode Ray Tube experiment
• Led to the Plum Pudding Model

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Ernest Rutherford - 1909

• Discovered the nucleus
• Nucleus
• Small tiny very dense center of atoms
• Where most the atoms mass is located
• Atoms are mostly empty space where electrons are
  found
• Conducted the Gold Foil experiment

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Niels Bohr - 1913

• Electrons move around the nucleus of atoms in
  definite paths.
• Electrons jump between levels from path to path.
• Bohrs model

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Most Recent Atomic Theory

• Schrodinger and Heisenberg
• Electron paths cannot be predicted.
• Electrons are likely to be found in regions
  around the nucleus called electron clouds.
• Called the electron cloud model.

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Recent Discoveries

• Chadwick
• Neutrons exist in the nucleus of atoms
• Neutrons have no charge and the mass equal to
  protons
• Gell-Mann
• Protons and neutrons are made of smaller
  particles called quarks

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Atomic Number

• The number of protons inside the nucleus of the
  atom.
• In a neutral atom, is also to the number of
  electrons
• Determines the element.
• All atoms of an element have the same atomic
  number.

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Isotopes

• Atoms of elements that have the same number of
  protons (atomic number) but a different number of
  neutrons inside the nucleus.

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Mass Number

• The total number of protons and neutrons in an
  atoms nucleus.
• Protons Neutrons Mass Number
• Practice If an atom has 12 protons, 14 neutrons
  and 12 electrons, what is its mass number?
• Practice online

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Atomic Mass Unit - amu

• Unit of measurement for the mass of subatomic
  particles.
• 1 amu 1.7 X 10 -24 They are TINY!!!
• .000000000000000000000017 grams
• Proton 1 amu
• Neutrons 1 amu
• Electrons almost zero (TINIEST particle with
  the least mass)
• Most mass is in the nucleus with protons and
  neutrons
• Otherwise atoms are mostly EMPTY SPACE

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Atomic Mass

• The weighted average of the masses of all the
  naturally occurring isotopes of an element.
• Average of Protons Neutrons of all an elements
  Isotopes Atomic Mass

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Ions

• Charged particles that form during chemical
  changes.
• Form when one or more valence electrons are
  transferred from one atom to another.

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Ions are Charged! or -

• Atoms that lose electrons become positive ions.
• Atoms that gain electrons become negative ions.
• Cl gains an electron from Na to form NaCl -
• Cl ion is negative - more electrons (-)
• Na ion is positive - more protons ().

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The Charge of an atom

• To find the charge of an atom, find the number of
  protons () and the number of electrons (-)
• Represent the electrons as a negative number
• Add the protons and electrons to find the charge
• Ex Calcium atom has 12 protons and 10 electrons.
  What is the charge of this atom?
• Answer 12 proton 10 electrons
• 12 (-10) 2
• This ion is represented as Ca2

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More practice with charge

• What is the charge of a copper atom with 26
  electrons?

• What is the charge of a Sulfur atom with 18
  electrons?

• Ans
• 29 protons () 26 electrons (-)
• 29-263
• Cu3

• Ans
• 16 protons () 18 electrons (-)
• 16-18-2
• S-2

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Energy Levels - Electron Clouds

• Regions around the nucleus where electrons are
  arranged.
• Electrons further away from the nucleus have more
  and more energy.
• Each level or cloud can hold a specific of
  electrons.
• 1st level - 2 electrons
• 2nd level - up to 8 electrons

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Valence Electrons

• The electrons in the outermost energy level
  (electron cloud).
• Very important because they determine how an
  element will react with other substances

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Review