CHAPTER 2 Atoms and Elements 1 Atoms Dalton s Atomic Theory - 1808 1. -Element is composed of small, indivisible particles called atoms. 2. -Atoms of an element have identical properties that differ from those of other elements. 3. -Atoms cannot be created, destroyed, or transformed -Compounds are formed when atoms of different elements combine in whole-number ratios. 4. -Atom ratios are constant in a given compound. 5. Chemical Reactions rearrange and recombine atoms but do not destroy them. 2 Structure of the Atom 1. The atom is mostly empty space. 2. It contains a very small, dense center called the nucleus. 3. Nearly all of the atom s mass is in the nucleus. 4. The nuclear diameter is 1/10,000 to 1/100,000 times less than atom s radius. 3
Fundamental Particles Three fundamental particles make up atoms. The following table lists these particles together with their masses and their charges. P article M ass (am u ) C h arg e E lectron (e - ) 0.00054858-1 P roton (p,p + ) 1.0073 +1 N eutron (n,n 0 ) 1.0087 0 4 Elements Elements substances that cannot be decomposed into simpler substances via chemical reactions Elemental symbols found on periodic chart First letter capital, second letter lower case C, Ca, Co CO is not an element. 5 6
Atomic Number The atomic number is equal to the number of protons in the nucleus. Sometimes given the symbol Z. Numbered consecutively on the periodic table The atomic number determines the element. The elements differ from each other by the number of protons in the nucleus. The number of electrons in a neutral atom is also equal to the atomic number. For charged species there are more electrons if it is negative and less electrons if it is positive 7 8 Mass Number and Isotopes Mass number is given the symbol A. A is the sum of the number of protons and neutrons. Z = proton number N = neutron number A = Z + N A common symbolism used to show mass and proton numbers is A Z E for example 14? N, 63? 12 6 C, Cu, 18 8 48 20? Ca, 197 79 Au 9
Mass Number and Isotopes How many protons and neutrons are in the following? 16 23 + 8O 11Na 18 8 O 238 92 236 92 U U 40 20 82 35 32 16 Ca Br S 2 2+ 10 Mass Number and Isotopes Give the number of protons, neutrons and electrons and the correct element symbol 24 12 15 7? 200 79?? 11 Isotopes Isotopes are atoms of the same element but with different numbers of neutrons. Isotopes have different masses and A values but are the same element. One example of an isotopic series is the hydrogen isotopes. 1 H or protium is the most common hydrogen isotope. one proton and no neutrons 2 H or deuterium is the second most abundant hydrogen isotope. one proton and one neutron 3 H or tritium is a radioactive hydrogen isotope. one proton and two neutrons 12
The Atomic Weight Scale and Atomic Weights The atomic weight of an element is the weighted average of the masses of its stable isotopes Example: Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63 Cu with a mass of 62.9 amu, and 30.9% 65 Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place. 13 The Atomic Weight Scale and Atomic Weights atomic weight = (0.691)(62.9 amu) + (0.309)(64.9 amu) 14424443 14424443 63 65 Cu isotope Cu isotope atomic weight = 63.5 amu for copper 14 Atomic Mass The atomic mass of an element on the periodic table is the weighted average of the masses of its stable isotopes For example H = 1.008 amu Calcium = 40.078 amu We will use these masses later for chemical calculations 15
Atomic Weights Weighted average of the masses of the isotopes Tells us the atomic masses of every known element. How do we know what the values of these numbers are? 16 A number of atoms, ions, or molecules that is large enough to see and handle. A mole = number of things Just like a dozen = 12 things One mole = 6.022 x 10 23 things Avogadro s number = 6.022 x 10 23 Symbol for Avogadro s number is N A. 17 Molar mass - mass in grams numerically equal to the atomic weight of the element in grams. H has an atomic weight of 1.00794 g 1.00794 g of H atoms = 6.022 x 10 23 H atoms Mg has an atomic weight of 24.3050 g 24.3050 g of Mg atoms = 6.022 x 10 23 Mg atoms 18
19 20 Calculate the mass of a single Mg atom in grams to 3 significant figures.? g Mg = 21
Calculate the mass of a single Mg atom, in grams, to 3 significant figures.? g 1 mol Mg atoms Mg = 1 Mg atom 23 6.022 10 Mg atoms 24.30 gmg = 4.04 10 1 mol Mg atoms 23 g Mg 22 Calculate the number of atoms in onemillionth of a gram of Mg to 3 significant figures.? Mg atoms = 23 Calculate the number of atoms in onemillionth of a gram of Mg to 3 significant figures.? Mg atoms = 1.00 10 6 23 6.022 10 Mg atoms 1 mol Mg atoms g Mg 1 mol Mg 24.30 g Mg = 2.48 10 16 Mg atoms 24
How many atoms are contained in 1.67 moles of Mg?? Mg atoms = 25 How many atoms are contained in 1.67 moles of Mg? 23 6.022 10 Mg atoms? Mg atoms= 1.67 mol Mg 1 mol Mg = 1.00 10 24 Mg atoms 26 How many moles of Mg atoms are present in 73.4 g of Mg? 27
Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? 1mol Mg atoms? molmg= 73.4 g Mg 24.30g Mg = 3.02 molmg YOU MUST KNOW HOW TO DO THESE PROBLEMS 28 29 1869 - Mendeleev & Meyer Discovered the periodic law The properties of the elements are periodic functions of their atomic numbers. 30
Groups or families Vertical group of elements on periodic table Similar chemical and physical properties Period Horizontal group of elements on periodic table Transition from metals to nonmetals Three regions Metals, nonmetals and metalloids 31 Period Horizontal group of elements on periodic table Transition from metals to nonmetals 32 Groups or families Vertical group of elements on periodic table Similar chemical and physical properties 33
Stair step function on periodic table separates metals from nonmetals. Metals are to the left of stair step. Approximately 80% of the elements Nonmetals are to the right of stair step. Approximately 20% of the elements have one side of the box on the stair step. Properties between metals and 34 nonmetals Periodic trends in metallic character More Metallic More Metallic Periodic Chart 35 Chemical properties of metals 1. -Outer (valence) shells contain few electrons 2. -Form cations by losing electrons 3. -Form ionic compounds with nonmetals 4. -Solid state characterized by metallic bonding -Conductors (electricity and heat) -Malleable - hammered -Ductile drawn -Typically solids (except mercury) 36
The Periodic Table: Metals Group IA metals Alkali metals Li, Na, K, Rb, Cs, Fr Group IIA metals Alkaline earth metals Be, Mg, Ca, Sr, Ba, Ra Group 3 12 Transition metals Lanthanides Actinides 37 Chemical properties of nonmetals 1. -Outer shells contain four or more electrons 2. -Form anions by gaining electrons (- charge) 3. -Form ionic compounds with metals and covalent compounds with other nonmetals 4. -Form covalently bonded molecules; noble gases are monatomic 5. -Insulators 6. Noble gasses have full shells 7. Poor conductors 8. Typically gasses or solids (Br 2 liquid) 38 Group VIIA nonmetals halogens F, Cl, Br, I 39
Group VIA nonmetals Chalcogens O, S, Se, Te 40 Group VIIIA nonmetals noble, inert or rare gases He, Ne, Ar, Kr, Xe, Rn 41 Group 16 nonmetals - O, S, Se, Te Group 17 nonmetals -halogens F, Cl, Br, I, At Group 18 nonmetals -noble, inert or rare gases He, Ne, Ar, Kr, Xe, Rn 42
Group 13 Boron Group 14 Carbon Group 15 Nitrogen Straddle the metal/ nonmetals 43 44