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Chapter 17. Properties of Atoms & the Periodic Table Sec. 1: Structure of the Atom. Each element has a chemical symbol used to abbreviate the chemical name.

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Chapter 17

Chapter 17

Properties of Atoms & the Periodic Table

Sec 1 structure of the atom
Sec. 1: Structure of the Atom

  • Each element has a chemical symbol used to abbreviate the chemical name.

  • Chemical Symbol—consists of 1 capital letter or 1 capital letter plus 1 or 2 lower case letters.

  • This system is used world-wide, so everyone knows what the symbols mean.

Atomic components
Atomic Components

  • Atom—the smallest piece of matter that retains the properties of the element.

  • Atoms are composed of protons, neutrons, and electrons.

  • Protons & neutrons are found in the small, positively charged nucleus.

  • Protons—particles with a charge of +1

  • Neutrons—neutral particles (no charge)

  • Electrons—particles with a charge of -1


  • The # of protons determines the type of atom.

  • How many protons do you see? This is an atom of what element is it?

Quarks even smaller particles
Quarks—Even Smaller Particles

  • Electrons are not made of smaller particles, but protons & neutrons are.

  • Protons & neutrons are made of smaller particles called quarks.

  • Scientists have found 6 different quarks.

  • Protons are made of 3 quarks tightly held together—neutrons are made of a different arrangement of 3 quarks.

Models of the atom
Models of the Atom

  • Atoms are difficult to visualize, so we use models to represent them.

  • Democritus proposed the idea of atoms in 400 B.C. His idea was not accepted for 2000 years

  • In the 1800s, John Dalton proved atoms existed.

    • He believed atoms were solid spheres.

  • The model of the atom has been changing ever since.

The electron cloud
The Electron Cloud

  • We now believe that electrons are found in an electron cloud.

  • Electron Cloud—the area around the nucleus where electrons are likely to be found.

  • The electron cloud is much larger than the nucleus.

  • It is impossible to tell exactly where an electron will be inside the cloud.

Sec 2 masses of atoms
Sec. 2: Masses of Atoms

  • Most of the mass of an atom is in the nucleus.

  • Protons & neutrons are about the same size.

  • Electrons are much smaller.

  • Atomic number—the number of protons in an atom. (always a whole number)

    • Atoms of different elements have different #’s of protons & different atomic #’s.

    • The atomic # of an element is on the periodic table

Mass number isotopes
Mass Number & Isotopes

  • Mass Number—the sum of the # of protons & the # of neutrons.

    • Mass # = # of neutrons + atomic #

  • If you know mass # & atomic # you can find the # of neutrons.

    • # of neutrons = Mass # - Atomic #

  • Not all atoms of the same element have the same # of neutrons.

  • Isotopes—atoms of the same element with different numbers of neutrons

Isotopes atomic mass
Isotopes & Atomic Mass

  • Different isotopes of elements have different properties.

  • You can distinguish isotopes by writing the name of the element followed by the mass #.

    • Ex. Carbon-12 and Carbon-14

  • Each element has an average atomic mass.

  • Average atomic mass (or atomic mass)—the weighted average mass of the mixture of isotopes. (found on the periodic table)

  • Atomic mass is always closest to the most abundant isotope.

Sec 3 the periodic table
Sec. 3: The Periodic Table

  • Periodic Table—an organized list of all known elements that are arranged according to their properties.

  • The 1st person to organize elements was Dmitri Mendeleev in the 1800s.

  • Mendeleev organized the elements by their atomic mass and left spaces for unknown elements.

The modern periodic table
The Modern Periodic Table

  • Mendeleev’s table was mostly correct, but it is more accurate to organize elements in order of increasing atomic number.


  • Groups (or families)—vertical columns on the periodic table.

    • They are numbered 1-18.

    • Elements in each group have similar properties.


  • Periods—horizontal rows of elements on the periodic table.

    • Periods are numbered 1-7

    • Elements increase by one proton as you move from left to right across a period.

Electrons the periodic table
Electrons & The Periodic Table

  • The periodic table organizes elements based on where their electrons are located.

  • Electrons (e-)—are located in different energy levels around the nucleus.

  • Elements in the same group have electrons arranged similarly which gives them similar properties.

Electron shells
Electron Shells

  • The number of energy levels or electron shells is determined by the period number.

  • Period 1: 1 electron shell and can hold 2 e-

  • Period 2: 2 electron shells & can hold 8 e-

  • Period 3: 3 electron shells & can hold 8 e-

  • As you move down the periodic table, 1 electron shell is added each time.

  • The outer electron shell must be full (usually with 8 e-) to be stable.

Valence electrons
Valence Electrons

  • Valence electrons are electrons in the outer energy level

  • We can predict the # of valence electrons for certain groups

  • Groups 3-12 cannot be easily predicted, there are too many exceptions to the rule









Electron dot diagrams
Electron Dot Diagrams

  • You can show the number of electrons in the outermost electron shell by using an electron dot diagram.

  • Dot diagrams use valence electrons which are the electrons in the outer electron shell.

  • Electron Dot Diagram—uses the symbol of the element and dots to represent the valence electrons.