Atomic Structure and the Periodic Table

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All Matter is Made of AtomsHydrogen is the most

common atom of our universe

Types of atoms in Earth’s Crust Iron 5%, Aluminum 8%,

Silicon 28%, Oxygen 47%, Other 12%

Types of atoms in HumansNitrogen 3%, Hydrogen 10%,

Oxygen 61%, Other 26 %

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Names and Symbols of Elements

Each element has its own symbol

Some elements use the first letter of the name: hydrogen (H), Sulfur (S),Carbon (C)

Other elements use the first letter of the name plus another letter: aluminum (Al), Platinum (Pt), Zinc (Zn)

The first letter is always capitalized and the following letters are lower case.

Early Greek Philosophers determined that atoms are the

building blocks of matter.

John Dalton (1766–1844)

John Dalton’s theory of the atom started out as a solid sphere with no charges

Proposed the atomic theory by investigating atomic weights of atoms

J.J. Thomson determines that an atom is made up of negative electrons

embedded in a sea of positive charges .

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Ernest Rutherford did some experiments with thin metal foils and

found that the positive charge is located within a central nucleus

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Neils Bohr worked under Rutherford but found problems with his theory. He

ultimately determined that Electrons are in circular orbits with increasing energy

levels.

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The modern atomic model shows that electrons occupy regions of space

whose shape is described by complex mathematical equations. (James

Chadwick)

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History of Atomic TheoryJohn Dalton’s theory of the atom started out as a solid

sphere with no charges.

Then J.J. Thomson figured out there were positive and negative charges in an atom.

Rutherford determined that the positive charges (protons) were located in the center of the atom and the negative charges (electrons) were scattered around the nucleus

Bohr’s theory said that the protons are in the middle and the electrons travel in specific energy levels and orbits around the nucleus

Modern model- protons and neutrons in nucleus, electrons on energy levels

ReviewAn atom is made up of protons (+), neutrons (no charge), and electrons(-).

The protons and neutrons are found in the nucleus

There has to be an equal number of protons and electrons because atoms have no net charge!

Atomic mass is the number of protons and neutrons

Atomic number is the number of protons (which is the same as the number of electrons)

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Vocabulary

Atom: the smallest particle of an element that has the chemical properties of the element

Nucleus: found in the center of the atom and contains the protons and neutrons

Proton: a positively charged particle found in the nucleus of an atom

Neutrons: an uncharged particle found in the nucleus of an atom

Electron: negatively charged particles that move around outside the nucleus of the atom

Isotopes: atoms of the same element that have a different number of neutrons. Chlorine atoms have 17 protons, but some atoms of chlorine have 18 or 20 neutrons these atoms are the isotopes of chlorine

Atoms form IonsIons: formed when an

atom loses or gains one or more electrons(- or + charge)

Cation: formed when an atom loses an electron (+ charge)

Anion: formed when an atom gains an electron (-charge)

Elements are organized by similarity

Modern Periodic Table organized by the atomic # of the elements

Dmitri Mendeleev began organizing elements by their physical and chemical properties (1860’s)

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Periodic Table of the ElementsMendeleev

produced the first periodic table

Called the periodic table because a periodic, or repeating pattern of properties of the elements

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Periodic TablePeriod: each row of the

periodic table is called a period. If you read from left to right one proton and one electron are added from one element to the next

Group/Family: Each column of the table is called a group or family. Elements in a group share similar properties. Groups/Families are read from top to bottom www.chem4kids.com

Atomic Size on the Periodic Table

Left to right atomic size decreasesTop to bottom atomic size increases

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More Properties of Periodic Table

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Periodic Table has distinct regionsReactive: indicates how likely an element

is to undergo a chemical change

Most elements are somewhat reactive and combine with other materials

The most reactive are in groups (up/down) 1 and 17

The least reactive are in group (up/down) 18

Elements combine by the outside electrons All of the electrons in the combining elements do not interact with

each other to form compounds….

Valence Electrons: Only the electrons in the element’s outside energy level interact with each other.

The most stable configuration has 8 electrons in the outer energy level.

Elements in group 1 have 1 electron in outside energy level and elements in group 17 have 7 electrons in outside energy level so they react with each other easily to form compounds and fulfill the 8

electron stable configuration.

MetalsMost elements are metals

Metals are elements that conduct electricity and heat, have shiny appearance, and can be shaped by pounding (malleability), bending, or being drawn into a thin wire (ductility)

Metal typesReactive metals: Group (up/down) 1 most reactive

Transition Metals: Group 3-12 (up/down) generally less reactive than most metals

Rare Earth Elements

Top row of the two rows of metals that are outside of the main periodic table

Also known as Lanthanides because they follow the element lanthanum (La) on the table

Scientists once thought these metals were available only in tiny amounts on the Earth

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Actinide

• bottom row of the two rows of metals that are outside of the main periodic table

• The Actinide series is all radioactive and some are not found in nature.

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NonmetalsNonmetals: the elements on the right side of the

periodic tableMany are gases at room temperature, dull

surfaces on the solid nonmetals, cannot be shaped by ductility or malleability

Halogens

Elements in group 17 7 valence electrons

Greek “forming salts

Very reactive non-metals that easily form compounds with metals. These compounds are known as salts.

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Noble Gases

Group 18 on the periodic table

8 valence electrons

Noble or inert because they almost never react with other elements

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Metalloids

Have properties of both metals and nonmetalsLocated on either side of the zigzag line

separating metals and nonmetalsMost common is Silicon

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Radioactivity

Radioactivity: the process by which the nucleus of an atom releases energy and particles

Marie Curie was the first person to isolate two radioactive elements (polonium and radium)

An isotope is radioactive if the nucleus has too many or too few neutrons

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Radioactive DecayRadioactive atoms

produce energy and particles from their nuclei

The identity of these atoms changes because the # of protons changes. (radioactive decay)

Occurs at a steady rate characteristic to each isotope

The amount of time for one-half of the atoms to decay is called the half-life of the isotope

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Radioactive Decay

Parent decays into daughter isotope. Combination of both is 100%

Parent starts at 100% and decays to 50%100% 1 half-life to 50% (daughter 50%)50% 2 half-lives to 25% (daughter 75%)25% 3 half-lives to 12.5% (daughter 87.5%)12.5% 4 half-lives to 6.25% (daughter 93.75%)