Intro to Atoms
Atoms: the basic particle in which all elements are
made
Nucleus: The central core of an atom containing
protons and neutrons
In the nucleus are:
• Proton: small, positively charged particle in the
nucleus of an atom ( + symbol)
• Neutron: Neutral charged particle in the nucleus
of an atom
Outside the Nucleus:
• Electron: tiny, negatively charged particle that
moves around the nucleus of an atom
Laws of Science
Law of Conservation of Matter
• Matter cannot be created or destroyed
Law of Conservation of Mass
Established by French Chemist Antoine Lavoisier
• In a chemical reaction, the mass of the
products equals the mass of the reactants.
THIS IS EXTREMELY IMPORTANT WHEN
BALANCING EQUATIONS
What’s the MATTER?
Matter: anything that has mass and takes up
space.
Mass: measurement of how much matter is in
an object
Element: a substance that cannot be broken
down into any other substances by chemical or
physical means
Compound: a substance of 2 or more elements
Mixture: 2 or more substances that are mixed
together, but NOT chemically combined
Atomic Models
Early Models/Theories of the Atom:
Dalton’s Atomic Model:
- All matter is composed of atoms
- Atoms cannot be made or destroyed
- All atoms of the same element are identical
- Different elements have different types of
atoms
- Atoms of 2 or more elements can join
together to form a compound
Modern Atomic Model – NOT ON
YOUR PAPER!
• Electrons form a negatively charged cloud
around the nucleus
• Cannot determine the location of an electron
at any given time
Atomic Models continued…
•
•
•
•
•
•
•
JJ Thomson’s Model:
Atom is positively charged
Discovered Electrons
Rutherford’s Model:
Protons and the nucleus
Electrons orbit around the positively charged nucleus
Chadwick’s Model:
Discovered neutrons
Bohr’s Model:
Electrons move in specific layers (shells)
Electrons move when atoms absorb or give off energy,
moving from one shell to another
Atoms and Elements
Atomic number
• number of protons in an element
• Number of electrons the element has
Atomic mass: mass of one atom of the element
How to calculate neutrons: atomic mass # - atomic
number
Valence electrons: electrons that can be
transferred from one atom to another or may be
shared between atoms
Chemical symbol: symbol for element (H –
Hydrogen) (C – Carbon)
Periodic Table
Dmitri Mendeleev
• Created first Periodic Table
• Arranged elements in order of increasing atomic
mass
• Placed similar elements in the same group
according to their reactions
Periods: a horizontal row in the P.T.
Groups: vertical columns in the P.T. – also known as
families due to similar characteristics
Groupings
•
•
•
•
•
•
Metals (Alkali , Alkali Earth)
Nonmetals
Nobel Gases
Transition Elements
Halogens
Common Elements
Valence Shells
Group 1 = 1 valence electron
Group 2 = 2 valence electrons
Group 13 = 3 valence electrons
Group 14 = 4 valence electrons
Group 15 = 5 valence electrons
Group 16 = 6 valence electrons
Group 17 = 7 valence electrons
Group 18 = 8 valence electrons (full shell)
Properties of Metals
• Classified by its physical properties such as
shininess, malleability, ductility, and
conductivity.
Malleable: can be hammered flat or into other
shapes
Ductile: can be pulled out into a long wire
Conductivity: ability to transfer heat from one
object to another
Metals continued…
Chemical properties: ability of a pure substance to
change into another substance.
Reactivity: The speed in which an element
combines or reacts with other elements
Corrosion: the wearing away of metal due to a
chemical reaction
Metals can be considered an alloy which is a
mixture of a metal with one other element
(usually found together in nature)
Physical and Chemical Properties
Physical
Chemical
• Def: a change that does not
result in the formation of
any new substances
• Examples:
Dissolving sugar in water
Melting ice cubes
Boiling water
Crumbling Paper
• Def: a change that
produces one or more new
substances
• A chemical reaction will
take place
• Burning paper
• Corrosion
• Rusting
• Milk or eggs going BAD
Nonmetals
•
•
•
•
•
Lack the properties of metals
Poor conductors of electricity and heat
Reactive with other elements
Dull and brittle (break easily)
Good insulators
Metalloids & Noble Gases
Metalloids
• Metalloids has
characteristics of both
metals and nonmetals
• Semiconductors:
substances that can conduct
electricity under some
conditions
Noble Gases
• Unreactive elements
• Exist in Earth’s atmosphere