Transcript Atomic theories and Valence Electrons

ATOMIC THEORIES AND VALENCE
ELECTRONS
ATOMIC THEORIES
• Dalton thought that atoms were like smooth, hard balls that could not
be broken into smaller pieces.
ATOMIC THEORIES
• Thomson suggested that atoms had negatively charged electrons
embedded in a positive sphere.
ATOMIC THEORIES
Bohr ModelEverything
moved
around
nucleus
RutherfordAtom mostly empty
space
ATOMIC THEORIES
Rutherford was surprised that a few particles were deflected
strongly. This led him to propose an atomic model with a
positively charged nucleus.
ATOMIC THEORIES
• Through the first part of the twentieth century, atomic models
continued to change.
Cloud Model- 1920’s
Electrons move rapidly every
which way
WHAT DOES IT MEAN TO BE REACTIVE?
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We will be describing elements according to their reactivity.
Elements that are reactive bond easily with other elements to make compounds.
Some elements are only found in nature bonded with other elements.
What makes an element reactive?
– An incomplete valence electron level.
– All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level
(This is called the rule of octet.)
– Atoms bond until this level is complete. Atoms with few valence electrons lose them during
bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.
VALENCE ELECTRONS
• Number of E- on the outer shell (the outside ring of the onion) of
atom, which determines reactivity of the atom
• Noble gases: 8 valence e- except He(helium) has 2= stability
– Elemental square info (stats)
• Stability- Is not actively seeking any other elements (nope is not
dating, is okay being alone because it has everything it needs)
• Example: Oxygen has 6 valence e- = not stable
– Actively seeking other elements (yep, dating but not exclusive,
has been seen with hydrogen and calcium)
VALENCE ELECTRONS
• The number of valence electrons in an atom of an element determines
many properties of that element, including the ways in which the
atom can bond with other atoms.
• Atoms usually react in a way that
• makes them more stable
– Scenario A: The number of valence e- increases to 8
– Scenario B: The atom gives up loosely held valence e(usually 1 or 2 valence e-)
LEWIS DOT STRUCTURE
• Shows the valence electron dot structures of atoms and bonding that
occurs among atoms
Yes ,this is Gilbert Lewis
WHAT DOES THAT MEAN TO ME?
• With a Lewis dot structure, you can show the valence e- of the atom
• AND…How bonding occurs among different atoms!
PRACTICE LEWIS DOT STRUCTURES
• Li
• Al
• B
• S
• Cl
• Ca
• K
• Kr
BONDING
• Chemical Bond- the force of attraction that holds 2 atoms together
as a result of the rearrangement of e- between them
• The number of valence e- determines whether or not atoms will bond
together
Would be the bonding
enforcers of the atom
world
BONDING