Mark S. Cracolice Edward I. Peters Mark S. Cracolice The University of Montana Chapter 5 Atomic Theory: The Nuclear Model of the Atom

5.1 Dalton’s Atomic Theory Dalton’s Atomic Theory (1808) 1. Each element is made up of tiny, individual particles called atoms. 2. Atoms are indivisible; they cannot be created or destroyed. 3. All atoms of each element are identical in every respect. 4. Atoms of one element are different from atoms of any other element. 5. Atoms of one element may combine with atoms of other elements, usually in the ratio of small whole numbers, to form chemical compounds.

5.1 Dalton’s Atomic Theory The atoms are neither created nor destroyed in chemical reactions, but simply arranged differently to form the products.

5.1 Dalton’s Atomic Theory Law of Multiple Proportions When two elements combine to form more than one compound, the different masses of one element that combine with the same mass of the other element are in a simple ratio of whole numbers.

Subatomic Particles Goal 3 Identify the three major subatomic particles by symbol, charge, and approximate atomic mass, expressed in atomic mass units.

5.2 Subatomic Particles Electron Symbol:e or e – Fundamental charge:1– Mass (g):9 × 10 –28 g Mass (atomic mass unit): u Location:Outside nucleus Discovered:1897 by Thomson

Subatomic Particles Proton Symbol:p or p + Fundamental charge:1+ Mass (g):1.673  10 –24 g Mass (u): u Location:Inside nucleus Discovered:1919 by Rutherford

Subatomic Particles Neutron Symbol:n or n 0 Fundamental charge:0 Mass (g):1.675  10 –24 g Mass (u): u Location:Inside nucleus Discovered:1932 by Chadwick

5.3 The Nuclear Atom

The Nuclear Model of the Atom An electron with a mass of 1/1837 u could not have deflected an alpha particle with a mass of 4 u. Rutherford concluded that each gold atom contained a positively charged mass that occupied a tiny volume. He called this mass the nucleus.

5.3 The Nuclear Atom The Nuclear Model of the Atom 1. Every atom contains an extremely small, extremely dense nucleus. 2. All of the positive charge and nearly all of the mass of an atom are concentrated in the nucleus. 3. The nucleus is surrounded by a much larger volume of nearly empty space that makes up the rest of the atom. 4. The space outside the nucleus is very thinly populated by electrons, the total charge of which exactly balances the positive charge of the nucleus.

5.3 The Nuclear Atom TThe diameter of an atom is approximately 10,000 times the diameter of its nucleus.

5.3 The Nuclear Atom Planetary Model of the Atom (1911) Electrons travel in circular orbits around the nucleus, much like planets move in orbits around the sun.

5.4 Isotopes Every atom of any particular element has the same number of protons, which is called the atomic number, Z. Atoms are electrically neutral, the number of electrons in an atom therefore must be equal to the number of protons.

5.4 Isotopes All atoms of any particular element are not identical; the number of neutrons may be different. Atoms of the same element that have different numbers of neutrons—different masses—are called isotopes.

5.4 Isotopes An isotope is identified by its mass number, A: Mass number = A = Total number of protons + neutrons Mass number = # of protons + # of neutrons A = Z + N

5.4 Isotopes Name of an Isotope Elemental name–Mass number Examples: What is the name of the carbon atom with 6 protons and 6 neutrons? Mass number = =12, so the name is carbon-12 What is the name of the carbon isotope with 7 neutrons? Mass number is = 13, so the name is carbon-13

5.4 Isotopes Symbol of an Isotope Known as a nuclear symbol Example: What are the nuclear symbols for carbon-12 and carbon-13?

5.5 Atomic Mass Masses of atoms are expressed in atomic mass units, u. The u is defined as 1 u  1/12 the mass of one carbon-12 atom 1 u  mass of 1 nuclear subatomic particle

5.5 Atomic Mass Percentage Abundance of Some Natural Isotopes SymbolMass (u)Percent 1 H H C12 (exactly) C K K K

5.5 Atomic Mass This is the mass spectrum of neon. The relative abundance plotted on the y-axis is the percentage of each isotope found in a natural sample of the pure element. The mass-to-charge ratio, m/z, is plotted on the x-axis. Since this plot shows 1+ ions only, m/z is the mass of the isotope, expressed in u.

5.5 Atomic Mass Atomic mass (of an element): The average mass of all atoms of an element as they occur in nature. Example: Chlorine has two natural isotopes: 75.78% is chlorine-35 at u and 24.22% is chlorine-37 at u. What is the atomic mass of chlorine? Solution: × u = u × u = u u

5.6 The Periodic Table Periodic Table of the Elements A table that arranges the elements in order of increasing atomic number. Elements with similar properties appear in the same column.

5.6 The Periodic Table

The Periodic Table Sample box from the periodic table, representing sodium.

5.6 The Periodic Table Periods Horizontal rows in the periodic table. Numbered 1–7, top to bottom (numbers usually not printed). Groups (or Chemical Families) Vertical columns in the periodic table. U.S. numbering: A groups and B groups IUPAC numbering: 1–18, left to right

5.6 The Periodic Table Main group elements (sometimes called representative elements) Elements in the U.S. A-groups Transition elements Elements in the U.S. B-groups Metals Elements on the left of the stair-step line Nonmetals Elements on the right of the stair-step line

5.7 Elemental Symbols

5.8 Elemental Symbols Memorize the 35 name–symbol pairs given in Fig Look at the location of each element in the periodic table while you work on memorization—it will help you remember the names and symbols. Whenever a chemical symbol has two letters, the first letter is always capitalized and the second letter is always written in lowercase.

Homework Homework for chapter 5: 17, 19, 21, 27,29, 31, 39, 41, 54