Atomic Structure Outline
Matter

Anything that has mass and takes up space

Matter can take many forms and is not always visible to the eye

Matter can change form
 Matter is made of atoms

Matter can neither be created nor destroyed; it just changes form - Law of
Conservation of Matter
Atoms

Tiny particles that make up matter

They are so small that 1 million atoms lined up side by side are equal to the thickness of a human hair
 “atom” comes from a Greek word that means “cannot be divided”

Atoms are made of small subatomic particles called protons, electrons, and neutrons
Proton

Positively charged particle

Located in the nucleus of an atom

Mass = 1 atomic mass unit

Number: the number of protons equals the number of electrons
Electron

Negatively charged particle

Located outside the nucleus of an atom

Mass is almost 0 (1/2000 of a proton)

Number: the number of electrons equals the number of protons
Neutron

Neutral particle, no charge

Located in the nucleus of an atom

Mass = 1 atomic mass unit

Number: the number of neutrons varies
Nucleus

Contains most of the mass of an atom
 Total number of particles in the nucleus is equal to the number of protons plus the number of neutrons
Model of the Atom

Protons and neutrons are found in the nucleus, the dense center of an atom

Nucleus is positively charged -protons are positively charged and neutrons have no charge

Electrons are found in a cloud around the positively charged nucleus

The electrons are very far away from the nucleus, so the atom is mostly empty space
Nucleus
 Most of the mass of the atom is located in the nucleus because electrons are so small compared to mass of protons and neutrons
Electrons
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
Electrons are arranged in energy levels around the nucleus, these are sometimes called energy shells

Electrons are negatively charged particles

Lowest energy level is closest to the nucleus and can contain only 2 electrons

Higher energy levels, further from the nucleus can contain more electrons
 Level 2 can hold 8 electrons, level 3 can hold up to 18, and level 4 up to 32

There are up to 7 energy levels for electrons
Types of Matter - Elements

Most kinds of matter are made of combinations of a basic group of building blocks called elements

Element - matter made up of only one type of atom

Natural elements

There are about 112 known elements today; 90 of these are naturally occurring elements, the rest are synthetic

Naturally occurring elements are found in nature
Synthetic elements

Synthetic elements are man-made in laboratories. These elements may exist naturally in stars, but on Earth they exist only when made in a lab

Synthetic elements are unstable
Periodic table

Elements are organized into a chart called the periodic table

They are organized by the number of protons in their nuclei

Mendeleev came up with the idea of classifying elements into a table
Element name and symbol

Each element has a name and an abbreviation known as its atomic symbol

Atomic symbols consist of 1, 2, or 3 letters. The first letter of the symbols is capitalized and the rest are lower case

New synthetic elements have the 3 letter symbol that represents their number and later are assigned a 2 letter symbol

For example Element 114 was called Ununquadium, Uuq, until it got its final name Flerovium, Fl
Atomic number
 The atomic number of an element indicates the number of protons in the nucleus of that element

Atoms are electrically neutral

The number of protons is equal to the number of electrons
Atomic mass of an atom

The atomic mass is a number that indicates the mass of the atoms of that element in atomic mass units, symbolized by the letter u

Atomic mass is equal to the number of protons + the number of neutron in the nucleus
Information on the periodic table
 Element name -----> Chlorine

Atomic number ---->17

Atomic symbol ----> Cl

Atomic mass ------>35.453
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Isotopes

All the atoms of an element have the same number of protons

There are different forms of an element called isotopes

Isotopes differ from each other because they have different numbers of neutrons

Isotopes have the same number of protons, but different numbers of neutrons
 Isotopes have different masses

C-12 and C-14 are isotopes of carbon

C-12 or Carbon-12, has a mass of 12 u , 6 protons and 6 neutrons

C-14 or Carbon-14, has a mass of 14 u , 6 protons and 8 neutrons

Isotopes are named by writing the name or symbol for the element followed by a hyphen and the atomic mass of the element

Ag-107 is silver with an atomic mass of 107, protons 47, neutrons 60
Average atomic mass

Because elements have various isotopes, the atomic mass reported in the Periodic
Table is an average of the masses of the various isotopes of the element

The amounts (percentages) of each isotope in a sample is accounted for when the average atomic mass is calculated
Ions

Atoms that have the same number of electrons and protons are neutral and have no charge

Sometimes atoms can be positively or negatively charged – atoms that have a charge are called ions

Ions with more electrons than protons are negatively charged

Ions with more protons than electrons are positively charged
Ions: anions

Negative ions are called anions

O
2-
, Oxygen ion with 8 protons and 10 electrons, has a charge of -2
Ions: cations

Positive ions are called cations

Mg
2+
Magnesium ion with 12 protons and 10 electrons, it has a charge of +2
Atomic identity
 Number of protons controls the identity of an element

Change the number of protons and you change to a new element
Atomic reactivity

Number of electrons controls the reactivity of an element

Atoms can add or lose electrons and still keep their identity

Atoms that add or lose electrons are charged and are called ions
Periodic Table

Mendeleev, a Russian scientist first organized all the elements known in the late
1800’s

He discovered repeating patterns in chemical properties
 He arranged the elements in order of increasing atomic mass
Modern Periodic Table
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
The periodic table is a table of the chemical elements in which the elements are arranged in order of atomic number in such a way that the periodic properties
(chemical periodicity) of the elements are made clear.

Elements are arranged in order of increasing atomic number

Increase in atomic number from left to right
Modern Periodic Table -Periods

Rows are called periods (horizontal)

Elements in the same period have the same number of energy levels for their electrons
Modern Periodic Table - Groups

Columns are called groups or families (vertical)

Elements in the same column have similar chemical properties

They have different numbers of electrons, but the same number of outer (valence) electrons
Modern Periodic Table
 Metals are to the left of the periodic table

Non-metals to the right

Metalloids are stair steps on right, between metals and non-metals
Periods

Numbered from 1 to 7

6 th
and 7 th
periods also contain the rows at the bottom of the table
Groups

Numbered from 1 to 18

Also called families

Each group of elements has characteristic chemical and physical properties that can assist in their identification
Group 1

Alkali metals

Easily react with water

1 valence electron

Hydrogen is in Group 1 because it has 1 valence electron, but it is not a metal
Group 17
 Halogens

Extremely reactive

7 valence electrons

Nonmetals

Tend to form negative ions and gain 1 electron
Group 18

Noble or Inert Gases
 Extremely unreactive, usually don’t bond with other elements

8 valence electrons (He has 2)
 Outer energy level can’t hold any more electrons
 Nonmetals
Metals

Groups 1-12 and parts of 13-17

Shiny or lustrous in appearance, hard, malleable, ductile (can be pulled into wires)
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
Conduct heat and electricity very well

Tend to form positive ions and give away or share 1 to 4 electrons

Most of the elements in the Periodic Table are metals

Find them on the left and the center of the Table
Nonmetals
 Can be gases or solids at room temperature

Belong to Groups 14 - 18

Find them on the upper right corner of the Periodic Table

Soft, brittle, and dull in appearance

Poor conductors of heat or electricity

Can share electrons or gain 1, 2, or 3 electrons to form negative ions
Metalloids

Select elements in Groups 13-17

B, Si, Ge, As, Sb, Te, Po, and At

Found along the boundary between metals and nonmetals, along a stairstep
 Not all scientists agree as to the exact elements in this group

Can be shiny or dull, soft or hard, malleable or brittle

Can conduct electricity, but not as well as metals (semi-conductors)
Chemical Reactivity

An example of chemical reactivity is when two or more elements combine to form compounds or molecules (if two of the same elements bond together)
Inorganic Compounds

Compounds of metal atom(s) and one or more nonmetal atoms

Often form ionic bonds with metal cation(s) (+) and nonmetal anion(s) (-)

Result in a neutral compound, also called a salt
Organic Compounds

Compounds that do not usually contain metal atoms

Often have C and H atoms bonded together by covalent (shared electrons) bonds

Also contain O, N, and S
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Summary
Elements are substances that cannot be broken down into smaller components by chemical means.
The Periodic Table of Elements is a table that organizes elements according to their physical and chemical properties.
Elements with similar physical and chemical properties are grouped together on the table.
For example, elements with metallic properties are grouped on the left side of the table while elements with nonmetallic properties are grouped on the right side of the table. The columns of the Periodic Table are referred to as groups and the rows are referred to as periods. The elements increase in atomic number from left to right.
The Periodic Table separates elements into metals, nonmetals, and metalloids. All of the elements on the left side of the border that runs through Groups 13-17 are metals with the exception of hydrogen (H). The elements on the right side of the Periodic Table are nonmetals.
Finally, the elements between the nonmetals and the metals are the metalloid elements.
Metals and nonmetals have different chemical properties from each other. For example, they react differently when combined with other substances. Metals added to hydrochloric acid
(HCl) generate bubble and heat as they reacted. Alternatively, when nonmetals are added to HCl, no visible chemical reaction takes place.
Elements from metal and nonmetal groups have different physical and chemical properties. One difference in physical properties is the ability to conduct or transmit electricity.
Elements that are metals have the ability to conduct electricity while elements that are nonmetals do not.
An atom is the smallest particle of an element that still has all the properties of that element. Atoms are composed of three different types of subatomic particles. In the nucleus of the atom are the protons and the neutrons. Protons have a positive electric charge while the neutrons have no electrical charge (they are neutral). Orbiting the nucleus are the atom’s electrons. They are small subatomic particles that carry a negative electrical charge.
An element’s atomic number is equivalent to the number of protons in its atoms’ nucleus or the number of electrons normally orbiting the nucleus. In addition, the number of neutrons likely to be found in the nucleus is equal to the element’s atomic mass minus its atomic number.
A metalloid is an element that can have the properties of both metals and nonmetals.
Metalloids can be found on the border of the metals and nonmetals of the Periodic Table of the Elements. The metalloids are boron (B), silicon (S), arsenic (As), tellurium (Te), germanium (Ge), antimony (Sb), polonium (Po), and astatine (At).
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