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2.1 Matter
Universe is made of matter
 Matter exists in one of 3 states
 Solid – definite shape & volume
 Liquid – definite volume, no definite
shape
 Gas – no definite volume, no definite
shape
2.1 Matter
Elements
 Elements – substance that cannot be
broken down by chemical or physical
means
 Over 100 elements are known
 Use symbols ex: H = hydrogen
2.1 Matter
Atoms
 Smallest particles of matter
 Have all the characteristics of an element
 The nucleus is the central part of an atom
and contains
• Protons: positive charge; mass = 1 amu
• Neutrons: neutral; mass = 1 amu
 Atomic mass = number of protons AND
neutrons in the nucleus
2.1 Matter
Atoms
 Energy levels, or shells
• Surround the nucleus
• Contain electrons
•Electrons: negative charge, 1/1836 amu
 The atomic number = number of protons in
the nucleus of an atom. Also tells us the number
of electrons.
Model of an Atom
Each energy level can hold a certain
number of electrons. The farther
away from the nucleus, the more
electrons the energy level can hold
3
2
1
The number of electrons
each level can hold is
determined by using the
equation 2(n2) where n =
the number of the energy
level
Nucleus
3rd energy level = 2(n2) =
2(32) = 2(9) = 18 electrons
2nd energy level = 2(n2) =
2(22) = 2(4) = 8 electrons
1st energy level = 2(n2) =
2(12) = 2(1) = 2 electrons
2.1 Matter
Periodic Table
 Group Number = number of valence
electrons in each element in that group
(column)
 Period Number = number of energy
levels containing electrons for every
element in that period (row)
Chemical Symbol Info
Atomic number
Chemical symbol
Element name
Atomic mass
Carbon
Try Your Own…
• Magnesium (Mg)
• Helium (He)
• Sulfur (S)
Ions
• When an atom gains or loses electrons it
becomes an ion
• Gains a positive or negative charge
• Example = Lithium
What are the most reactive
• VALENCE!
• Outermost energy level!
• Draw a Lewis Dot structure
e?
2.1 Matter
Isotopes
 Isotopes of an element have the same number
of protons but varying numbers of neutrons.
 Have different mass numbers: the sum of the
neutrons plus protons
 Many isotopes are radioactive and emit energy
and particles.
2.1 Matter
Why Atoms Bond
 Atoms are likely to form chemical
bonds with one or more atoms to fill
their outermost energy level (valence!)
 Compounds form when atoms are more
stable in a combined form
 Most stable elements = Noble gases
(group 18)
2.1 Matter
Types of Chemical Bonds
1. Covalent bonds form when atoms share
electrons.
2. Ionic bonds form between positive and
negative ions. There is a transfer of
electrons!
3. Metallic bonds form when metal ions
share electrons.
Covalent Bond
Metallic Bond
Ionic Bond