Dalton’s Atomic Theory

1. Dalton’s Atomic Theory • Elements are composed of tiny particles called atoms. • All atoms of a given element are identical. • All carbon atoms have the same chemical and physical properties. • Atoms of a given element are different from those of any other element. • Carbon atoms have different chemical and physical properties than sulfur atoms.

2. Symbols for the Elements • Symbolized with one or two letters • First letter is capitalized, second is small Carbon: C Bromine: Br • Common elements and symbols in Table 4.3

3. Elements • Robert Boyle (1627-1691) • Elements: cannot be broken down into atwo or more simpler substances • 155 elements: 88 natural

4. Dalton’s Atomic Theory • Atoms of different elements combine to form compounds.

5. Dalton’s Atomic Theory • Law of Constant Composition: all samples of a compound contain the same proportions (by mass) of the elements that form the compound. • Atoms are indivisible by chemical processes. • All atoms present at beginning are present at the end. • Atoms are not created or destroyed, just rearranged in chemical reactions. • Atoms of one element cannot change into atoms of another element. • Cannot turn lead into gold by a chemical reaction

6. Writing Formulas of Compounds • Each element is represented by its symbol. • The number of each type of atom is indicated by a subscript written to the right of the element symbol. • If only one atom is present, do not include a subscript. • If polyatomic groups are present in the molecule, they are written inside parentheses if more than one group is present. • Examples: H2O, NaCl, KNO3, Mg(NO3)2

7. J. J. Thomson’s “plumb pudding” model of the atom (1910) • Atom contains positive particles that balance the negative charge of the electrons.

8. Rutherford’s Gold Foil Experiment • www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

9. Rutherford’s Nuclear Model (1911) • The atom contains a tiny dense center calledthe nucleus. • The nucleus is essentially the entire massof the atom. • The nucleus is positively charged. • It is composed of protons (positive charge) and neutrons (no charge) • balances the negative charge of the electrons. • The electrons move around in the empty space of the atom surrounding the nucleus.

10. The Modern Atom (cont.)

11. Components of an Atom

12. The Modern Atom • Atoms are composed of three main pieces: protons, neutrons, and electrons. • The nucleus contains protons and neutrons. the hydrogen atom (H) the helium atom (He)

13. Isotopes • All atoms of an element have the same number of protons. • The number of protons in an atom of a given element is the same as the atomic number. • Found on the periodic table • Atoms of an element with different numbers of neutrons are called isotopes.

14. Isotopes (cont.) • All isotopes of an element are chemically identical. • Undergo the exact same chemical reactions • Isotopes of an element have different masses. • Isotopes are identified by their mass numbers. • Mass number = # of protons + # of neutrons • Isotope symbols: X = the symbol of the element A = the mass number Z = the atomic number (number of protons) A - Z = # of neutrons

15. Isotope Examples

16. Other Examples

17. The Modern Periodic Table

18. Properties of Metals • Good conductors of heat and electricity • Malleability (thin sheets) • Ductility (wires) • Shiny • All are solids at room temperature except mercury (Hg)

19. Properties of Nonmetals • Poor conductors • Not malleable or ductile • Exist in various physical states: solids – carbon, phosphorus liquids – bromine gases – hydrogen, oxygen, helium

20. Metalloids • Show a mixture of metallic and nonmetallic properties • Examples:

21. Problem Give the symbol and classify as a metal, nonmetal or metalloid: • Silver • Sulfur • Silicon • Barium

22. Natural States of Elements • Most elements are solids at room temperature. • Group 8 Noble gases: • Diatomic molecules:

23. Diatomic Molecules

24. Allotropes of Carbon

25. Ions • Cations: ions that have a positive charge • Form when an atom loses electrons • Anions: ions that have a negative charge • Form when an atom gains electrons • Cations and anions attract each other.

26. Atomic Structures of Ions • Metals form cations. • For each positive charge the ion has 1 less electron than the neutral atom. • Na = 11 e-, Na+ = 10 e- • Ca = 20 e-, Ca+2 = 18e- • Cations are named the same as the metal. sodium Na  Na+ + 1e- sodium ion calcium Ca  Ca+2 + 2e- calcium ion

27. Atomic Structures of Ions (cont.) • Nonmetals form anions. • For each negative charge the ion has 1 more electron than the neutral atom. • F = 9 e-, F- = 10 e- • P = 15 e-, P3- = 18e- • Anions are named by changing the ending of the name to –ide. • Fluorine F + 1e- F- fluoride ion • Oxygen O + 2e- O2- oxide ion

28. Ionic Charges and Compounds • Charges on the ions of some elements can be predicted from the periodic table. • Cations and anions usually form simultaneously to yield an ionic compound. • When ions are formed the number of protons and neutrons does not change. • There must be a net charge of zero.

29. Ionic Charges and Compounds (cont.)

30. Formulas of Ionic Compounds • The formula of an ionic compound can be determined by balancing the positive charge of the cation(s) with the negative charge of the anion(s) to yield a net charge of zero. • Ba2+ and Cl- • K+ and P3- • Ca2+ and O2- • Mg2+ and N3-