1 Chapter 2 Atoms, Molecules and Ions A. Chemical Elements and Compounds B. Atomic Particles C. Isotopes D. Atomic Mass and Molecular Mass E. Nomenclature HW #P1 P1 is covered on Quiz 1 and Exam 1.
2 2.1 The Atomic Theory of Matter 2.2 The Discovery of Atomic Structure – Your Portions to Read. 2.3 The Modern View of Atomic Structure - The Nuclear Atom 2.4 Atomic Weights 2.5 The Periodic Table A. Chemical Elements and Compounds Chemical Elements 90 naturally occurring Everything is composed of these elements. Atoms are the building blocks of matter. Each element is made of the same kind of atom. A compound is made of two or more different kinds of elements. Elements combine to form compounds. If one divides an element to the smallest unit, which retains identity atom?
3 Atoms combine to form molecules. H + H + O H H O water macroscopic scale atomic scale elements atoms compounds molecules
7 If two elements, A and B, form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers. Dalton predicted this law and observed it while developing his atomic theory. MC Problem 2.13: A chemist finds that 30.82 g of nitrogen will react with 17.60 g, 35.20 g, 70.40 g, or 88.00 g of oxygen to form four different compounds. Calculate the mass of oxygen per gram of nitrogen in each compound. How do the numbers support Dalton's atomic theory? These masses of oxygen per one gram nitrogen are in the ratio of 1:2:4:5 - small whole numbers and thus obey the law of multiple proportions, as stated in Dalton's theory. Since atoms are indivisible, they must combine in ratios of small whole numbers.
8 B. Atomic Particles • Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. • Most of the volume is empty space. • Atoms are very small; • 1 – 5 Å or 100 – 500 pm. (1 Å = 10 -10 m) • Other subatomic particles (protons and neutrons) were discovered. • Each atom is composed of particles. • Protons (+1) and electrons ( – 1) have a charge; neutrons are neutral. Protons and neutrons have essentially the same mass (relative mass 1). The mass of an electron is so small we ignore it (relative mass 0). • Protons and neutrons are found in the nucleus; electrons travel around the nucleus. • Mass is in nucleus nuclear density is 10 13 g/cm 3 . Particle Mass ( g ) Atomic mass units Electrical charge ( C ) Relative charge electron 9.109×10 −28 0.0005486 −1.602×10 −19 − 1 proton 1.673×10 −24 1.007276 +1.602×10 −19 +1 neutron 1.675×10 −24 1.008665 0 0