Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

1. Chapter 4Chemical Foundations:Elements, Atoms, and Ions

2. Elements • Over 112 known: 88 found in nature, others are man made. • Each element has a unique one- or two-letter symbol

3. Elements (cont.)

4. Elements (cont.)

5. 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.

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

7. 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 • View Early Discoveries

8. Formulas Describe Compounds • A compound is a distinct substance that is composed of atoms of two or more elements. • Compounds are identified by the number and type of each atom in the simplest unit of the compound. • Molecules or ions

9. 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 • View Describing Chemical Formulas

10. What Are Atoms Made Of? • J.J. Thomson investigated a beam called a cathode ray. • He determined that the ray was made of tiny negatively charged particles we now call electrons.

11. The Electron • Tiny, negatively charged particle • Very light compared to mass of atom • 1/1836th the mass of a H atom • Move very rapidly within the atom • Atoms of different elements all produce electrons; therefore electrons are a fundamental unit of atoms.

12. The Proton • If negative electrons exist, must also have positive particles to balance the charge and make the atom electrically neutral • Assume “Plum Pudding Model” - electrons suspended in a positively charged electric field

13. Rutherford’s Nuclear Model • The atom contains a tiny dense center calledthe nucleus. • The volume is about 1/10 trillionth the volume of the atom. • The nucleus is essentially the entire massof the atom. • The nucleus is positively charged. • The amount of positive charge of the nucleus balances the negative charge of the electrons. • The electrons move around in the empty space of the atom surrounding the nucleus.

14. Components of an Atom

15. The Modern Atom • Atoms are composed of three main pieces: protons, neutrons, and electrons. • The nucleus contains protons and neutrons.

16. The Modern Atom (cont.)

17. 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.

18. 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 = # protons + # neutrons

19. Isotopes of Carbon • 12C has 6 protons (atomic number ) and 6 neutrons (atomic mass number = 6 + 6 = 12) • 13C has 6 protons and 7 neutrons (atomic mass number = 6 + 7 = 13) • 14C has 6 protons and 8 neutrons (atomic mass number = 6 + 8 = 14)

20. Elements • Arranged in a pattern called the periodic table • Position on the table allows us to predict properties of the element

21. Elements (cont.) • Metals • About 75% of all the elements • Lustrous, malleable, ductile, conduct heat and electricity • Nonmetals • Dull, brittle, insulators • Metalloids • Also know as semi-metals • Some properties of both metals & nonmetals

22. The Modern Periodic Table • Elements with similar chemical and physical properties are in the same column. • Groups (Families) and Periods

23. The Modern Periodic Table (cont.)

24. The Modern Periodic Table (cont.) • Main group = representative elements • “A” columns • Transition elements • All metals • Bottom rows = inner transition elements = rare earth elements • Metals • Lanthanides and actinides

25. Natural States of Elements • Gases: monatomic gases such as noble gases and diatomic gases such as O2 • Liquids such as Hg or Br2 • Solids such as metals or allotropes of carbon

26. Natural States of Elements (cont.)

27. 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 • Ions with opposite charges attract • Therefore cations and anions attract each other

28. Ions (cont.) • Moving ions conduct electricity. • Compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 total charge.

29. 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

30. 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

31. 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.

32. Ionic Charges and Compounds (cont.)

33. 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.

34. Periodic Table • Periodic Table Tutorial • http://www.wwnorton.com/college/chemistry/gilbert/overview/ch6.htm#covalent_bond