Transcript ATOMIC THEORY & BONDING

4.1 Atomic Theory & Bonding
What is an Atom?
 smallest particle of an element that still
has the properties of that element
 An atom = proton(s) + electron(s) + neutron(s)
(PEN)
 Fun Fact:
50 million atoms, lined up end-to-end = 1 cm
An ELEMENT is made up of one type of atom
 The element, oxygen, is O
 IONS are atoms with a charge.
 The ion of oxygen is O2-
 Atoms can join together to form MOLECULES.
 The oxygen molecules are O2
 COMPOUNDS are made up of several (2+)atoms
 Hydrogen and oxygen are atoms/elements
 H2O is a compound
Structure of an Atom:
The nucleus is at the centre of an atom
 composed of protons (positive charge) and
neutrons (neutral charge)
Electrons (negative charge) exist in the space
surrounding the nucleus
Subatomic Particles:
 Atoms are made up of smaller particles
known as sub-atomic particles.
Name
Symbol
Charge
Location
Atomic Mass
Proton
p
1+
nucleus
1 AMU
Neutron
n
0
nucleus
1 AMU
Electron
e
1–
area surrounding
the nucleus
1/1836 (0)
Numbers to Remember :
 # of protons = # of electrons in every atom
AND ONLY IN ATOMS!!! (not ions)
 Nuclear charge = charge on the nucleus
= # of protons
 Atomic number = # of protons
= # of electrons in atoms
Families of the Periodic Table:
 Columns of elements are called groups, or families
 All elements in a family have…
 similar properties
 bond with other elements in similar ways
 have the same number of valence electrons
 Family names (on the periodic table!):
 Group 1 = alkali metals
 Group 2 = alkaline earth metals
 Group 17 = the halogens
 Group 18 = noble gases
 Periods are horizontal rows on the periodic table
INCREASING REACTIVITY
Where are the
following?
• Atomic
Number
• Period
• Group/Family
• Metals
• Non-metals
• Transition
metals
• Metalloids
• Alkali metals
• Alkaline earth
metals
• Halogens
• Noble gases
Periodic Table & Ion Formation:
 Atoms gain and lose electrons to form ions
 Metals lose electrons & become positive ions
(cations)
 Some metals can have more than one charge
(multivalent)
 ie. Iron, Fe, loses either 2 (Fe2+) or 3 (Fe3+)
electrons
 Non-metals gain electrons & become negative ions
(anions)
 Atoms do this in an attempt to have the same
number of valence electrons as the nearest noble
gas – to become stable
Bohr Diagrams:
 Bohr diagrams show how many electrons
appear in each electron shell around an
atom.
 Each shell holds a maximum number of
electrons (2, 8, 8, 18, 18)
 Electrons in the outermost shell are called
valence electrons
 Except for the transition elements, the last digit
of the group # = # of valence electrons
Note: Think of the shells as being 3D like spheres, not 2D like circles!
Bohr Diagrams
What element is this?
•It has 2 + 8 + 8 = 18
electrons, and therefore
18 protons
18 p
22 n
•It has 8 electrons in the
outer (valence) shell
Argon!
Bohr Diagrams for the first 20 elements
 Note: The noble gas
elements have full electron
shells, and are very stable.
Bonding Types:
 When two atoms get close together, their
valence electrons interact.
Covalent Bonds:
 Formed between two or more non-metals
 Electrons are shared between atoms
+
Hydrogen
Hydrogen fluoride
Fluorine
Electrons are shared
Ionic Bonds:
 Metals give electrons to non-metals (transfer of
electrons)
 cations (+ ions) and anions (- ions) form
 For example, lithium and oxygen form an ionic
bond in the compound Li2O
+
Lithium
Oxygen
Electrons are transferred from
the cations to the anion
Li+
O2Li+
Lithium oxide,
Li2O
Lewis Diagrams:
 Like simplified Bohr diagrams
 Only valence electrons are shown
 Dots representing electrons are placed around
the element symbols (on 4 sides, imagine a box
around the symbol)
 Electron dots are placed singularly, until the fifth
electron is reached, then they are paired.
Example:
Nitrogen atom
Lewis Diagrams:
 Note: the Lewis diagrams are the same
(except for the symbols) for elements in the
same family because they have the same
number of valence electrons
Lewis Diagrams for Ions:
 For positive ions: one electron dot is removed
from the valence shell for each positive charge
of the ion.
 For negative ions: one electron dot is added to
each valence shell for each negative charge of
the ion.
 Square brackets and the charge are placed
around each ion
Example:
Nitrogen ion
Lewis Diagrams For Ionic Bonds:
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Be
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Cl
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Cl
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•2+
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Be
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Cl
Each beryllium has two
Since Be wants to
electrons to transfer
donate 2 electrons and
away, and each
each Cl– wants to
chlorine wants one
accept only one, two
more electron
Cl– ions are necessary
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Cl
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Be
2+
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Cl
The ionic compound
Beryllium chloride is
formed
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Lewis Diagrams For Covalent Bonds:
 valence electrons are drawn to show sharing of
electrons.
 Remember: All atoms “like” to have a full valence shell
 The shared pairs (“bonding pairs”) of electrons are
usually drawn as a straight line
 “lone pairs” are the electrons not shared