Compounds (vs. elements?)

Transcription

1 I. Classify different forms of matter. Compounds (vs. elements?) A. Method based on temperature (Which side (l or r) is high temperature?) (States of matter) melting evaporation Bose-Einstein Condensate Solid liquid gas plasma freezing condensation B. A purity based method (of sorts) C. Element: Cannot be separated into simpler substances by chemical means. 1. copper (Cu) 2. magnesium (Mg) 3. All those substances on the periodic table 4. Review: What determines the identity of an element? Note: With respect to elemental identity, an atom with 6 p + and 6 n in its nucleus is considered to be the same type of atom as one with 6 p + and 8 n in its nucleus. These two atoms are said to both be of carbon. 5. Sometimes we talk about a substance composed of only one type of atom as being in its elemental state. Elemental state means the state in which that element exists in nature. The elemental state of: a) He, helium, is as a gas, b) Fe, iron, is as a solid c) Hg, mercury, is as a liquid (Not many elements exist as liquids in nature.)

2 Note: Seven elements are diatomic (two elements bonded covalently) in their elemental state. I never order broiled clams from Hardees. Also, phosphorous exists as P 4 and sulfur as S 8 D. Compounds: Pure substances formed when atoms combine in specific ratios. The combining is when the atoms form some kind of. 1. Sodium chloride, NaCl 2. Water, H 2 O E. Mixtures: Two or more types of substances mixed together in varying ratios. They can be separated by physical means. 1. Homogeneous: Uniform composition (also called a ) Example: 2. Heterogeneous: Non-uniform composition. Ex: II. Most matter on earth & in your body isn t in its elemental form. It is present as compounds or mixtures. A. If we consider the lecture room (or lab?), can you identify any matter that is in its pure elemental form? B. What about outside of the lecture room? 1. the blue stuff is... elemental vs. compound pure vs. mixture homogeneous vs. heterogeneous Fig. from 2. the white stuff the green stuff... C. Does classification of the stuff above depend on how big of a block of blue (white, green) stuff we chose to examine? III. Formation of two types of compounds from elements A. Elemental sodium (Na (s) ) reacting with chlorine (Cl 2(g) ) to form table salt (NaCl (s) ), an : 2 Na (s) + Cl 2(g) 2 NaCl (s) Not safe to do, but see: &

3 B. Important: 2 distinct things occur in these rxns. You must be able to recognize them as distinct. 1. First, e - are being transferred to convert atoms (or molecules) into ions: Na Na + + e - (ox) Cl e - 2 Cl - (red) metals tend to lose e - (give e - away), non-metals tend to gain e -. (Electronegativity: the relative ability of an element to attract electrons in a bond. Usually elements with high electronegativity tend to e -, and elements with low electronegativity tend to e -.) 2. Second, positively charged ions bind to negatively charged ions to form ionic compounds: Na + + Cl - NaCl 3. Another example: Elemental magnesium (Mg (s) ) reacting with oxygen (O 2(g) ) to form magnesium oxide (MgO (s) ): 2 Mg(s) + O 2 (g) 2 MgO(s) See: Two steps: 1. Mg(s) Mg e -, O e - 2 O 2-2. Mg 2+ + O 2- MgO positively charged ions are called negatively charged ions are called In the rxns shown above, a metal combined with a non-metal to form an ionic compound as the product a.k.a. a salt. The ions in the salt are held together by electrostatic attraction, + to -. C. Formation of the second type of compound! What happens when we combine two non-metals?

4 D. Hydrogen gas (H 2(g) ) reacting with oxygen (O 2(g) ) to form water (H 2 O (g) ): 2 H 2(g) + O 2(g) 2 H 2 O (g) 1. The Hindenberg was a air ship (specifically, a dirigible) whose buoyancy was provided by H 2 (g). A known risk associated with this technology was hydrogen reacting violently with oxygen. Is there a readily available source of the reactant O 2 on earth? Viewer warning, people died 2. In the rxn. shown above in, two non-metals combine to form a covalent compound. The product is a molecule. The atoms in the molecule are held together by covalent bonds. IV. Ionic bonds, ionic compounds, ionic compound formulas A. In an ion: # of p + # of e -. B. Ions can be simple or compound 1. A simple ion consists of one charged atom (for example Cl - ). 2. A compound ion has multiple atoms held together by covalent bonds and carries a charge. (for example NO 3 - ) C. Ionic bond refers to the electrostatic attraction between oppositely charged ions. What do like charged things do? My son s static electricity hair experience! D. Ionic compound formulas must have zero net charge. (No shock when you touch an ionic compound) 1. Determine charge of simple ions in ionic components from Periodic Table. How? 2. Want the minimum number of each ionic component that results in equal amounts of + and - charge.

5 Problem: Write ionic compound formulas for: 1. potassium chloride 2. calcium iodide 3. sodium phosphide 4. sodium phosphate 5. magnesium oxide 6. iron (II) nitrate Note: Although the ionic compound formula, NaCl, shows a 1 to 1 ratio of the ions, it is incorrect to think of a specific, directionally-oriented interaction between one Na + and one Cl -. You can see from the figure that each Na + is actually interacting equally with 6 Cl - ions (and vice versa). Most NaCl crystals contain many, many more ions than that shown below! Ions also attract & repel each other in aqueous solution, for example a solution of salt dissolved in water. In a solution, the H 2 O reduces the interaction strength between the ions significantly. In CHM 109 we will have some interest in ions and ionic bonds, but we will have more interest in covalent bonds. What is a covalent bond? A covalent bond is a shared e - pair!