• Substances containing only ONE kind of atom are
• CANNOT be broken down into smaller pieces
(by normal laboratory processes)

• In the early 1900s, scientists began to identify the particles that make up atoms (subatomic particles

• Every atom has a core called a nucleus, where the majority (99.9%, to be exact) of an atom's mass is held.
• Although the nucleus contains the majority of the mass of the atom, the nucleus is very small compared to the size of the whole atom, because most of the atom is empty space surrounding the nucleus.
• Within the nucleus are two types of smaller particles called protons and neutrons.
• The third type of particle that makes up the atom,
electrons, orbit around the nucleus in the electron cloud

• Positively charged particles found inside the
nucleus of an atom. Every atom of a particular element contains the same number of protons.
• Number of protons is unique to each element.
Each element has a unique atomic number, or a unique number of protons in its nucleus.
• Never changes for any given element.
– example, oxygen has an atomic number of 8. That tells us that oxygen always has 8 protons.

• Other particle found in the nucleus of an atom.
• Unlike protons and electrons, neutrons carry no electrical charge. neutrons are "neutral.”
• Atoms of a given element do not always contain the same number of neutrons.
– Atoms of an element that have a different number of neutrons in the nucleus are called isotopes of each other.

• Electrons are negatively charged particles that orbit around the outside of the nucleus in electron cloud.
• The mass of an electron is about 1/2000th of the mass of a proton or a neutron.
• The sharing or exchange of electrons between atoms forms chemical bonds, which is how new molecules and compounds are formed.

• How many protons are in that atom's
nucleus.
For example, oxygen has an atomic number of 8, meaning that there are 8 protons in the nucleus of an atom of oxygen. Copper's atomic number is 29, meaning that there are 29 protons in the nucleus of an atom of copper.
– Later, you'll see how the periodic table conveniently tells you each element's atomic number.

• Because atoms are so small, their masses cannot be measured in grams or milligrams.
• Instead, scientists have created the atomic mass unit (amu) to measure mass of subatomic particles. The mass of a proton or a neutron is about 1 amu. The mass of an electron, however, is about 1/2000 amu.

• To find the atomic mass of an atom, add the number of protons and neutrons in the
nucleus.
– Example: If an atom has 3 protons, 4 neutrons, and
3 electrons, the atomic mass is 7 amu, because you do not count the very small mass of the atom's electrons (1/2000 amu). Only add the number of protons and neutrons (each has a mass of 1 amu) in the nucleus.

• Question: Find the atomic mass of an atom that has 10 protons, 8 neutrons, and 10 electrons.

• Answer: 18 amu. Just add the protons and neutrons.

• 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.

• …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.

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

• Mendeleev wasn’t too far off.
• Now the elements are put in rows by increasing
• 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.

•When you look at the periodic table, you should notice that each box represents a different element, and each box contains vital information about the element, including its name, symbol, atomic number, and atomic mass.
»
»
»
6
»RR C
»
12.011
ATOMIC NUMBER
# of Protons
The element's symbol
Element’s name
ATOMIC Mass

• ROWS- Horizontal
• Contains different types of elements from different families NOT alike in properties
• Gradually change properties as you go across left to right.
• BUT there is a pattern
• From very reactive metals to metalloids to nonmetals to unreactive gas.

• Still a part of the table
• Separated out to make the table less wide and more user friendly!

• (Mendeleev did that on purpose.)
Why??
• They have the same number of valence electrons.
• They will form the same kinds of ions.

• 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.)

Are arranged in
Organized in order of increasing made up of
called called

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

• 1 st 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

• 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

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

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

• 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.

• 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.

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

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

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

• Most periodic tables contain a
which allows you to identify which elements are metals, nonmetals, and metalloids. Following are descriptions of each of the three types of materials.

• Most elements are metals. 88 elements to the
left of the stair step line are metals or metal like elements.
• Chemical Properties of Metals:
• Easily lose electrons
• Corrode easily. Corrosion is a gradual wearing away. (Example: silver tarnishing and iron rusting)

• Luster (shininess)
• Good conductors of heat and electricity
• High density (heavy for their size)
• High melting point
– Solid at room temperature
– Some require temperature increase of 3,400 C to melt them
• Except Mercury Hg, which is liquid at room temperature
• Ductile (most metals can be drawn out into thin wires)
• Malleable (most metals can be hammered into thin sheets)
• Several are attracted to magnets and can be made into magnets
(iron Fe, cobalt Co, and nickel Ni)

• Mixture= two or more substances mixed together
• Alloy= mixture of metals
– Combine the best properties of two or more metals
– Iron= rusts easily but mix with carbon, chromium, and vanadium = stainless steel
– Cooper= thin and malleable but mix with tin=
Bronze (last hundreds of years)

• Many of the very common elements
• Nonmetals are found to the right of the stair step line. Their characteristics are opposite those of metals.
• Chemical Properties of Nonmetals:
• Tend to gain electrons
• From compounds easily

• Opposite of metals
• No luster (dull appearance)
• Poor conductor of heat and electricity
• Brittle (breaks easily) low density
• Not ductile
• Not malleable
• Low density
• Low melting point
• Low boiling points
– Many are gases at room temperature

• Elements on both sides of the zigzag line have properties of both metals and nonmetals.
• Varying ability to conduct electricity
• Most common is Silicon Si
• Combines with Oxygen, O, to form familiar substances including sand, glass and cement

• Solids
• Can be shiny or dull
• Ductile
• Malleable
• Conduct heat and electricity better than nonmetals but not as well as metals

• valence electrons are the electrons contained in the outermost, or valence, electron shell of an atom .
• Based on the understanding of protons, neutrons and electrons, scientists are able to explain and predict how atoms will behave in interactions
• Modeled on the transferring of electrons
BETWEEN atoms

• Electrons involved in transferring or sharing
• The number of electrons available determines if element: gives up, shares or accepts electrons from other elements during reactions
– The fewer valence electrons an atom holds, the less stable it becomes and the more likely it is to react .
• Increase from left to right across period (row) of periodic table.

valence electrons in their outer energy level to be stable
• Others need 8 to be stable – usually.
• Electron dot diagrams- include the element symbol and dots to represent valence electrons
• Can use electron dot diagrams to help us determine stability-
– H is less stable than He because it has only 1 valence electron while He has 2 valence electrons

• They share, gain, or lose electrons to become stable
• Chemical bond- force that holds atoms together in a compound – caused by either exchanging or sharing electrons

• Elements in same groups have same number and arrangement of valence electrons and have similar properties.
• # of valence electrons help determine an element’s properties

Periodic table group
Group 1 (I) ( alkali metals )
Group 2 (II) ( alkaline earth metals )
Groups 3-12 ( transition metals )
Group 13 (III) ( boron group )
Group 14 (IV) ( carbon group )
Group 15 (V) ( nitrogen group )
Group 16 (VI) (oxygen halogens)
Group 17 (VII) ( halogens )
Group 18 (VIII or 0) ( noble gases )
* Valence electrons are not generally useful for transition metals.
** Except for helium , which has only two electrons.
5
6
3
4
7
8**
# Valence electrons
1
2
1 or 2*

• Since metals tend to lose electrons and nonmetals tend to gain electrons,
– metals and nonmetals like to form compounds with each other. These compounds are called ionic compounds.

• Chemical bond
• Attraction between opposite charges of ions of in an ionic compound
– The metal donates one or more electrons , forming a positively charged ion with a stable electron configuration .
– These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration.
– The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond.

• For example, common table salt is sodium chloride .
When sodium (Na) and chlorine (Cl
2
) are combined,
– The sodium atoms each lose an electron, forming a cation
(Na + ),
– The chlorine atoms each gain an electron to form an anion
(Cl ).
– These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).
– Na + ½Cl
2
→ Na + + Cl → NaCl

• When two or more nonmetals bond with each other, they form a covalent compound.
• Chemical bond
• Atoms share pairs of electrons
• Produces molecules

• Chemical Formula- tells how many of each element are present in a compound
– Consists of element symbols and subscripts
– Water has 2 hydrogen atoms and 1 oxygen atom

•
• SiO
2 silicon- 1 Oxygen-2
•
• C
12
H
22
O
11
Carbon- 12 Hydrogen-22 Oxygen-11
•
• N
2
O
Nitrogen- 2 Oxygen-1