Post on 25-Dec-2015
transcript
Atoms Atom = is the smallest particle of an
element Existence theorized and named by
Democritus in 4th century B.C.! Atomic Theory grew as a series of
models developed from experimental evidence, over time the theories and models were revised
Dalton’s Atomic Theory In 1808 Dalton developed the atomic
theory: Atoms cannot be divided (now false) All atoms of one element are exactly alike
(now false) Atoms cannot be changed into an atom of a
different element. Atoms cannot be created nor destroyed, only rearranged.
Atoms of different elements join in specific ratios to form compounds
Thompson’s Model In 1897, Thompson
discovered the electron, a negatively charged particle within an atom.
Proposed model of atom with negative charges scattered throughout a ball of positive charge – like berries in a muffin.
Rutherford’s Model In 1911,
Rutherford used his gold foil experiment to find the nucleus, a tiny region in the center which contained positively charged protons.
Bohr’s Model
In 1913, Bohr showed the electrons moved in orbits like planets orbiting around the sun.
Cloud Model In the 1920’s
scientists found electrons do NOT orbit around the nucleus like planets, instead they can be anywhere in a designated “cloud” region, called an energy level.
Modern Atomic Model
In 1932, Chadwick discovered the neutron, a neutral particle within the nucleus.
Modern model = at the center of the atom is a tiny nucleus containing protons and neutrons. Surrounding the nucleus is a cloudlike region of moving electrons.
Scientist/Model QUIZ Match the atomic structure/model with
the scientist: Dalton, Rutherford, Thompson, Bohr, Chadwick, Democritus
1. Orbiting planet model2. Gold foil experiment3. Nucleus4. Electron5. Proton6. Neutron7. Energy level8. “Atom”
Parts of the AtomNucleus: atom’s central core, made up
of protons and neutrons, is positive in charge
Proton (p+): subatomic particle that has positive charge, has some mass
Neutron (n): subatomic particle that has no charge or is neutral, same mass as proton
Electron (e-): subatomic particle that has a negative charge, relatively no mass
Comparison Chart
Atoms have no charge overall since protons balance out electrons.
Particle Symbol Charge Mass Location
Proton p+ +1 ~ 1amu Nucleus
Neutron n 0 ~ 1amu Nucleus
Electron e- -1 ~ 0amu Outside nucleus
Atomic Structure Atomic Number: number of protons in
the nucleus of an atom Atomic # = # of p+
Determines the identity of the element Periodic table is organized by atomic
number Ex: What is the atomic number of…
He ______ C ______ N ______ O ______
Summary:
Create a BRACE MAP to illustrate the structure of the ATOM Use the following words:electrons atom electron cloudNeutrons nucleus protons
I. Mendeleev’s Periodic Table By 1869, 63 elements had been
discovered. Mendeleev found a way to organize them.
He arranged them by atomic mass, the average mass of all the isotopes of an element.
He noticed a pattern of properties in the table and was able to predict where future elements would occur!
II.Modern Periodic Table
The modern periodic table is organized by the number of protons or atomic number.
The properties of an element can be predicted from its location on the periodic table.
According to periodic law, when elements are arranged this way, similarities in their properties will occur in a regular pattern.
III. Finding Your Way Around The Periodic Table:
Classes of Elements: Elements are classified as metals, semimetals,
or nonmetals. The zigzag line on the periodic table separates
the metals from the nonmetals
III. Finding Your Way Around The Periodic Table:
Periods: The horizontal rows. The properties of elements in a row follow a
repeating pattern as you move across each period.
III. Finding Your Way Around The Periodic Table:
Groups (Families): The vertical columns (top to bottom). Elements in the same group have similar
characteristics.
III. Finding Your Way Around The Periodic Table:
Reading the Data: Each square in the table gives: atomic number chemical symbol element name atomic mass
Chemical Symbol = representation of an element usually consisting of 1 or 2 letters
State of Matter
Periodic Table displays the state of matter element is in at room temperature
Solids: Most common on table Liquids: Only 2-5 total on table Gases: in upper, right hand corner
Classification Metals: elements that are shiny,
bendable, conduct heat and electricity well. Most common, take up left and middle of
table Nonmetals: elements that conduct heat
and electricity poorly. Located in upper, right corner of table
Metalloids: located in between metals and nonmetals, on “staircase” Semiconductors: element that conducts
fairly well
Properties of Metals The Reactivity of metals tends to decrease as you
move from left to right across the periodic table Physical Properties:
Luster (shiny) Malleability = material can be hammered or
rolled into sheets/shapes Ductility = material can be pulled out into wire Thermal conductivity = ability to transfer heat Electric conductivity = ability to transfer
electric current
Properties of Metals Chemical Properties:
Reactivity = ease and speed substance reacts with other substances Decreases as you move from
left to right on table! Corrosion = gradual wearing away
of a metal due to chemical reaction
Alkali Metals Group 1: Alkali Metals
React w/ other elements by losing 1 electron
Super reactive; always found in compounds, never alone in nature
Soft, shiny Ex: sodium, lithium,
potassium
Alkaline Earth Metals Group 2: Alkaline Earth Metals
Hard, gray-white, good conductor of electricity, fairly reactive
Form compounds found in limestone and in human body
React by losing 2 electrons Ex: magnesium, calcium,
barium
Transition Metals: Groups 3-12, Group that contains the
MOST elements Conduct heat and
electricity Hard, shiny, colorful Ex: copper, iron,
mercury, silver, gold, nickel
Transition Metals
Groups 13-15, some are metals (Aluminum, Gallium, Indium, Thallium, tin, lead, bismuth)
Never found uncombined in nature
Metals in Mixed groups
Synthetic Elements Synthetic elements are made by scientists
by forcing nuclear particles to crash into one another. The nuclei break apart quickly so this makes it
difficult to determine properties of newly discovered elements
Elements numbered 92 and greater Particle accelerator = moves atomic nuclei
at high speeds causing them to crash into each other, sometimes combine into single nuclei
Nonmetals Physical Properties:
Dull Brittle Poor conductor
of heat and electricity
Basically the OPPOSITE of metals!
Chemical Properties: Gain or share
electrons Metals and
nonmetals often react together
Nonmetals Located on the right side of table Abundant on Earth
Oxygen and Nitrogen make-up 99% of atmosphere
Carbon is in more compounds than any other elements combined!
Group 17: Halogens Very reactive Dangerous to humans Ex: Fluorine, Chlorine,
Bromine, Iodine, Astatine Group 18: Noble/Inert
gases: Unreactive Do not usually form
compounds Ex: Helium, Neon, Argon,
Krypton…
Semimetals/Metalloids Contains only 8 elements,
found along boundary between metals and nonmetals Have properties of both metals and nonmetals Ex: Boron, Silicon, Arsenic… Are semiconductors: conduct heat and
electricity under certain conditions Silicon used in computer chips to speed up
conduction
Radioactivity
Radioactive decay = atomic nuclei of unstable isotopes release fast-moving particles and energy.
Radioactivity = element which spontaneously emits radiation
First discovered by Becquerel in 1896 with uranium.
Types of Radioactive Decay Radioactive decay can produce 3 types of
radiation: Alpha Decay: an alpha particle consists of
2 protons and 2 neutrons and is positively charged. Can be stopped by a thin layer
Beta Decay: a neutron is converted into a beta particle, a fast-moving electron Can be stopped by thick material
Gama Decay: high-energy waves Can only be stopped by thick
concrete or lead
Uses of Radioactive Isotopes Radioactive isotopes can include the
tracing steps of a chemical reactions, industrial processes, and diagnosing and treating disease.