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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.