Discovery of electrons

Transcription

1 This week: What are atoms made of? How do you name compounds and molecules? Dalton s atomic theory 1806 A good theory: Explains all available data Predicts future results Well tested Is usually ignored/disgraced for a while Known natural laws in 1806: Discovery of electrons Law of conservation of mass: Lavoisier 1785 Law of constant composition: 1700 s Law of multiple proportions: Dalton Natural Law: Statement of WHAT happens, not why These laws led to Dalton s Atomic Theory Figure 2.4 The size of an atom Amu: atomic mass unit 1 amu = x g A specific carbon atom has exactly 12 amu All else is relative Figure

2 Sub atomic particles Atoms are really small! Atoms are really small Particle Proton Charge +1 Mass (g) 1.67 x10 24 Mass (amu) Table 2.1 Heaviest atom is only 4x10 22 g Only 1x10 10 m in diameter Electron x x10 4 Can t see with optical microscopes neutron x Gnat sized nucleus here, outer atom at Hwy 1 Atomic Force Microscopy Cu atoms holes Xe atom Fe on Cu Xenon on Nickel Multi-culturalism! 2

3 Making an atomic corral (iron on copper, IBM) Mass spectrometer Mass spectrum of Cl Are all atoms of an element created equally? Mass of Cl is amu from periodic table Figure 2.13 MS leads to discovery of p and n Mass spec Figure 2.14 Average atomic mass similar to GPA calculation 3 unit class = C (2 grade points) 5 unit class = A (4 grade points) Does GPA = 3? Atomic symbols Atomic number = # of protons in nucleus. Mass number = # of p plus n in nucleus At the Earth s surface, 98.93% C with amu 1.070% C with amu Calculate the average mass of C atoms 3

4 px Complete atomic Isotope symbols symbols m ± X is atomic symbol p is atomic number (# of??) m is mass number (# of?? +??) Charge shows result of electrons lost or gained Write atomic symbol for: P, Zn, common ion of Na On Periodic Table 3 Li Atomic # Atomic symbol Atomic mass have the same # p but different # n. # of protons define the element 11 6 C 12 6 C 13 6 C 14 6 C Concept Check-isotopes Can two atoms have the same mass but be different elements? Concept check: atomic symbols How many protons, neutrons and electrons in Phosphorus-31? What is the full atomic symbol for P-31 if it has gained 3 e How many protons, neutrons and electrons in Pu-239? What is the full atomic symbol for a n and 28 e? ion that has Concept check: atomic symbols How many protons, neutrons and electrons in Phosphorus-31? What is the full atomic symbol for P-31 if it has gained 3 e Discovery Radioactivity of Radioactivity Three types of radiation were discovered in the early 1900 s by Marie Curie Henri Becquerel How many protons, neutrons and electrons in Pu-239? What is the full atomic symbol for a 2 + ion that has 45 n and 31 e? Ernest Rutherford 4

5 α particles He nuclei β particles electrons γ rays high Energy X-rays Figure 2.8 Radioactivity is the process of nuclei changing spontaneously into other nuclei Nuclear decay is not affected by Temp, Pressure or time Radiation is useful for sterilization, killing cancer cells, and imaging tissues Relative Penetration power What can we do with atomic masses? α β γ Can be used to calculate relative amounts of a substance What is mass percent of fluoride in NaF? Can be extended to grams also: How many g of Na in 1.00 g NaHCO 3? 5

6 Types of compounds Compounds are two or more atoms bonded together. The chemical formula of a compound indicates which atoms are found in the molecule, and in what proportion they are found. Compounds consisting of are molecular compounds. Compounds consisting of are ionic compounds Molecules that contain two atoms of same element bonded together are called molecules. Molecules and Molecular Compounds diatomics Ionic Compounds Ions are charged atoms or molecules Ionic compounds (such as NaCl) are usually formed between metals and nonmetals. Prediciting Predicting charge Predicting Ionic Charge Figure 2.23 Figure 2.22 Naming ionic compounds Cation (+ ion) name goes first elemental cations are named as element Naming oxo-anion Inorganic Compounds Anion ( ion) goes second replace suffix of element with ide GaAs gallium + arsenic = examples from PT Follow same rules for Polyatomic ions Tranisition metal compounds: use Roman numerals Figure

7 Molecular compounds Molecular compounds exist as individual molecules Molecules stay intact when going from solid to liquid to gas, or when dissolving in a solvent Molecular formulas Molecules and Molecular Molecular Compounds compounds Molecular formula: actual ratio of elements in molecule C 6 H 12 O 6 Empirical formula: smallest whole # ratio of elements Molecules and Molecular Picturing Compounds molecules Rules for naming molecular compounds More metallic element s name comes first Metallic character increases going down or left When in doubt, put carbon first, or oxygen last Add to the 2 nd element s name Use to show how many atoms are in the compound Drop one letter of a-o or o-o, but not i i Examples Figure 2.21 Molecular compound prefixes Examples A compound with 2 N and 3 F Nitrogen is to the left, so elements are in order: Nitrogen fluoride Add prefixes: 7

8 Examples Name: N 8 Cl 7 CBr 4 S 7 O 5 STUDY hours per week Do more than you think you should You CAN succeed! Concept Check Naming Inorganic acids What is formula of hexaphosporus pentaselenide? What is name of O 2 F 5? Acids: a special class of compound, Have H in formula Names of acids are related to the names of anions: -ide becomes hydro-.-ic acid; -ate becomes -ic acid; -ite becomes -ous acid. examples Know methane through hexane: CH 4 CH 3 CH 3 CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 What is name of this compound: Figure 2.28 CH 3 CH 2 Cl 8

9 Ionic examples Make and name ionic compounds: Na and N Cu 2+ and NO 3 Co 3+ and CO 2 3 K and CN Ca and PO 4 3 Sr and MnO 4 Zn and SO 3 2 Concept Check: Write formulas for the following compounds Iron (II) hydride Lead (IV) phosphate Manganese (II) perchlorate Sodium hypochlorite Beryllium hydroxide Aluminum nitrite Lithium oxalate Magnesium cyanide Chromium (VI) bicarbonate Zinc sulfite 9