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Chapter 17

Chapter 17. Properties of Atoms & the Periodic Table http://www.youtube.com/watch?v=d0zION8xjbM&feature=fvw. Sec. 1: Structure of the Atom. Each element has a chemical symbol used to abbreviate the chemical name.

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Chapter 17

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  1. Chapter 17 Properties of Atoms & the Periodic Table http://www.youtube.com/watch?v=d0zION8xjbM&feature=fvw

  2. 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.

  3. 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

  4. Nitrogen • The # of protons determines the type of atom. • How many protons do you see? This is an atom of what element is it?

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

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

  13. Groups • Groups (or families)—vertical columns on the periodic table. • They are numbered 1-18. • Elements in each group have similar properties.

  14. Periods • 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.

  15. 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.

  16. 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.

  17. 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 4e- 6e- 8e- 1e- 2e- 3e- 5e- 7e-

  18. 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.

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