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Science 8- Atoms and the periodic table

Atoms and molecules
by

john krieger

on 22 October 2014

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Transcript of Science 8- Atoms and the periodic table

Structure of the Atom
A. Elements are abbreviated in scientific shorthand- usually the first letter or two of the element's name
B. Atom- smallest piece of matter that still has the properties of the element
C. Protons and neutrons are made up of smaller particles called quarks
D. Scientists use scaled - up models to represent atoms
1. Protons have an electric charge of 1+
2. Neutrons do not have an electrical charge
3. Electrons have an electric charge of 1-
4. Protons and neutrons are in the nucleus of an atom; electrons surround the nucleus
1. six quarks are know to exist; the sixth is called the top quark
1. Early models of atoms used a solid sphere
2. Current electron cloud model shows electrons traveling in specific energy levels around a nucleus of protons and neutrons
Masses of Atoms
A. Atomic mass- composed mostly of the protons and neutrons in the nucleus
B. Isotopes- atoms of the same element with different numbers of neutrons
1. The unit of measurement for atomic particles is atomic mass unit (amu) which is one- twelfth the mass of a carbon atom containing six protons and six neutrons
2. Atomic number- the number of protons in an atom; number of protons also identifies the element
3. The sum of the number of protons and neutrons in the nucleus of an atom is the mass number
1. Different isotopes have different properties
2. The number of neutrons is equal to mass number minus atomic number
3. the name of the element followed by mass number identifies the isotope
4. Average atomic mass is the weighted average mass of an elements isotopes
5. Average atomic mass is closest to its most abundant isotope
The Periodic Table
A. elements are organized in the periodic table by increasing atomic number
B. Vertical columns in the periodic table are groups of elements with similar properties
C. Periods- horizontal rows of elements that contain increasing numbers of protons and electrons
D. The same elements exist all over the universe
1. In the late 1800s Dmitri Mendeleev devised the first periodic table based on atomic mass
2. In 1913, Henry G. J. Moseley arranged the elements by atomic number rather than atomic mass
1. elements in the same group have the same number of electrons in their outer energy level
2. Each of the seven energy levels can have a maximum number of electrons
a. energy level one can contain at most 2 electrons
b. Energy level two can contain at most eight electrons
3. Each row in the periodic table ends when an outer energy level is filled
4. Electron dot diagrams use the element symbol and dots to represent outer energy level electrons
1. Elements are classified as metals, nonmetals, or metalloids (semimetals)
2. elements are synthesized in laboratories all over the world
1. Hydrogen and helium are the building blocks of other naturally occurring elements
2. Supernovas spread heavier elements throughout the universe
Properties of Atoms and the Periodic table
Mendeleev wasn’t too far off.
Now the elements are put in rows by increasing ATOMIC NUMBER!!
The horizontal rows are called periods and are labeled from 1 to 7.
The vertical columns are called groups are labeled from 1 to 18.

The Current Periodic Table

Elements in group 18
VERY unreactive, monatomic gases
Used in lighted “neon” signs
Used in blimps to fix the Hindenberg problem.
Have a full valence shell.

The Noble Gases

The Noble Gases

Elements in group 14
Contains elements important to life and computers.
Carbon is the basis for an entire branch of chemistry.
Silicon and Germanium are important semiconductors.

Carbon Family

Elements in group 13
Aluminum metal was once rare and expensive, not a “disposable metal.”


Boron Family

Second column on the periodic table. (Group 2)
Reactive metals that are always combined with nonmetals in nature.
Several of these elements are important mineral nutrients (such as Mg and Ca

Alkaline Earth Metals

1st column on the periodic table (Group 1) not including hydrogen.
Very reactive metals, always combined with something else in nature (like in salt).
Soft enough to cut with a butter knife

Alkali Metals

Columns are also grouped into families.
Families may be one column, or several columns put together.
Families have names rather than numbers. (Just like your family has a common last name.)

Families on the Periodic Table

The periodic table is the most useful tool to a chemist.
You get to use it on every test.
It organizes lots of information about all the known elements.

Why is the Periodic Table important to me?

The Periodic Table

Elements in group 17
Very reactive, volatile, diatomic, nonmetals
Always found combined with other element in nature .
Used as disinfectants and to strengthen teeth.

Halogens

Hydrogen belongs to a family of its own.
Hydrogen is a diatomic, reactive gas.
Hydrogen was involved in the explosion of the Hindenberg.
Hydrogen is promising as an alternative fuel source for automobiles

Hydrogen

Why??
They have the same number of valence electrons.
They will form the same kinds of ions.


Elements in the same group have similar chemical and physical properties!!
(Mendeleev did that on purpose.)

Groups…Here’s Where the Periodic Table Gets Useful!!

SOME PROBLEMS…
He left blank spaces for what he said were undiscovered elements. (Turned out he was right!)
He broke the pattern of increasing atomic weight to keep similar reacting elements together.

HOW HIS WORKED…
Put elements in rows by increasing atomic weight.
Put elements in columns by the way they reacted.


Dmitri Mendeleev: Father of the Table

…was a mess!!!
No organization of elements.
Imagine going to a grocery store with no organization!!
Difficult to find information.
Chemistry didn’t make sense.

Pre-Periodic Table Chemistry …

Elements in group 16
Oxygen is necessary for respiration.
Many things that stink, contain sulfur (rotten eggs, garlic, skunks,etc.)

Oxygen Family or Chalcogens

Elements in group 15
Nitrogen makes up over ¾ of the atmosphere.
Nitrogen and phosphorus are both important in living things.
Most of the world’s nitrogen is not available to living things.
The red stuff on the tip of matches is phosphorus.

Nitrogen Family

Elements in groups 3-12
Less reactive harder metals
Includes metals used in jewelry and construction.
Metals used “as metal.”

Transition Metals

Metals
Most elements on the periodic table are classified as metals
They can be found to the left of the zig-zag line

Metals have specific physical properties (characteristics)

shiny
malleable
ductile
conductive
shiny- reflect light

malleable- can be pounded into sheets
ductile- can be drawn into wires

conductive- able to transfer heat or electricity

Most are solid at room temperature

some metals are attracted to magnets

reactivity- the degree with which an element interacts with other elements.

reactive elements combine with other elements easily

The noble gasses on the far right of the periodic table do not react with ANYTHING!

Metals usually react by losing electrons, and become less reactive as you move from left to right on the periodic table

Some metals react with oxygen in the air, forming metal oxides, a process called corrosion.

Iron can combine with oxygen in the air to form Iron Oxide (rust)

Each group on the periodic table has similar physical and chemical properties

Group 1- alkali metals are so reactive that they are never found in pure (elemental) form in nature.

Group 2- alkali earth metals

Group 3 through 12- transition metals

Groups 13-15 combinations of metals, nonmetals, and metalloids.

Nonmetals and metalloids
Nonmetals are elements lacking the properties of metals
most are poor conductors, and reactive with other elements.
(many react with metals)
Those that are solids are dull and brittle
Group 14- the Carbon group is highly reactive
Most living (organic) things have a large amount of carbon
Carbon is the only nonmetals in the group
Group 15- Nitrogen Family
two nonmetals in the group are nitrogen and phosphorus
Group 16- the oxygen group
Group 17- The Halogens,
Group 18- the Noble gases
The Metalloids
Seven elements
Some characteristics of metals and of nonmetals

most important is the their varying ability to conduct electricity
this makes able to be used as semiconductors- substances that under some conditions can carry electricity, and under other conditions cannot carry electricity.
Semiconductors are used in the production of many electronics.
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