Unit 2A Notes

Mr. Fedell

A1/A2 - Properties make the difference/Physical and chemical properties Properties - characteristics that enable us to distinguish one kind of matter from another Ex: Rainbow Physical property - Properties that can be observed without changing the identity of the material Chemical property - a property that can be observed when changing a substance into a new substance Physical change - change in a substance which doesn’t change the substance into something new. Ex. cutting, grinding, melting (any changes of state are physical changes – boiling, condensing, freezing, subliming) Chemical change - a process where one or more substances are converted into other substances with different characteristics. 2 Na (s) soft, grey metal crystal reactant

+

Cl2 (g) green, poisonous gas reactant

→

2 NaCl (s) white, tasty product

Examples of chemical changes – milk souring, cooking eggs, burning paper, pouring acid on metals

Signs of a chemical change

Change in temperature, change in odor, change in color, forms a gas, forms a precipitate

A4 - The chemical elements Properties of Metals – Shiny (luster), Conduct electricity and heat, Malleable (able to be hammered into sheets), Ductile (able to be drawn into a wire), React with acids to produce Hydrogen gas Examples: Mg, Au, Ag, Na, Pb, Hg, etc. Properties of Nonmetals – the opposite of metals Examples: O, N, Cl, He, H, etc. Properties of Metalloids – some properties of metals/nonmetals They are: B, Si, Ge, As, Sb, Te, Po (you should be familiar with these) Example: Si shiny, conducts electricity (like metals) no reactivity with acid, not malleable, not ductile (like nonmetals)

A6/A8 - The periodic table / The pattern of atomic numbers Dimitri Mendeleev (Russian) - creator of the first periodic table in 1869, organized by atomic weight and “combining capacity”, created it for his students…what a nice guy Atomic weight - the mass associated with an element; determined using naturally occurring isotopes (we’ll get to that) Examples: H = lowest mass (1); O~16 times greater than H; S ~32 times greater than H Atomic Number - the number of protons in an element; dual purpose! How? Can also represent the number of electrons Proton - positively charged particle; determines “identity” of atom Neutron - neutral particle; determines weight of atom

Electron - negatively charged particle; determines charge of atom; located outside the nucleus Nucleus - positively charged center of atom; contains protons & neutrons

(Draw an atom) Mass number - the total number of protons and neutrons in an atom Represented as: 200Hg, Hg-200/80Br, Br-80 Isotope - atom with same number of protons but different numbers of neutrons Examples: C-12, C-13, C-14 (12C, 13C, 14C) Ion – a charged atom caused by more or less electrons Represented as: F-1, Zn+2 Cation- positively charged ion (lose e-) Examples: Metals Ag+, Mg+2,etc.

Anion- negatively charged ion (gain e-) Examples: Nonmetals Cl-, O-2

Practice: Calculate Protons, Neutrons, and Electrons for: Element Protons Neutrons Sodium Ne S-2 F-1 41 Ca 40 Ca

Electrons

A10 – The periodic table Know - how the modern periodic table is organized Modern periodic law - elements arranged in order of increasing atomic number Period - rows in the PT; do not have similar characteristics Group - columns in the PT; do have similar characteristics Examples: the noble gases Alkali metal - first group in the PT, contains most reactive metals, elements are soft (can be cut with a knife), not found alone in nature Examples: Li, Na, etc…Forms 1:1 ratio with halogens (NaCl, LiBr, etc.) and 2:1 ratio with oxygen (Na2O, Li2O, etc.) Alkaline earth metal - second group in the PT, contains 2nd most reactive metals Examples: Be, Mg, etc…Forms 1:2 ratio with halogens (MgCl2, CaF2, etc.) and 1:1 ratio with oxygen (BeO, MgO, etc.) Transition metals - elements in groups 3-12, harder, more brittle, form colored compounds, can be found alone in nature (coinage) Examples: Cu (penny), Ni (nickel), Au (gold coins), Ag (silver half-dollar) Halogens – group 17, most reactive of the nonmetals, not found alone in nature Examples: Cl, Br, I, F…the second half of HONClBrIF Noble gases – group 18, least reactive of all the elements Examples: He, Ne, Ar, Xe, Kr, Rd Metalloids…look back in the fact sheet (they make up a “staircase”) The rest is not in your vocab/facts sheet…time to take out your own notes Color PT showing grouping (below)

Families: Group 1: Alkali metal Group 2: Alkaline earth metal Groups 3-12: Transition metals

Groups 13-16(kind of): Metalloids (B, Si, Ge, As, Sb, Te, Po) Group 17: Halogens Group 18: Noble gases

Which elements are more alike? 1. Chlorine and Phosphorus or Chlorine and Iodine 2. Magnesium and Sodium or Potassium and Sodium 3.

Arsenic and Antimony or Arsenic and Phosphorus or Arsenic and Germanium

A11 - Predicting properties Mendeleev’s claim to fame – predicting properties of elements not yet discovered – he actually left spaces in the PT for unknown elements Called them “eka-” meaning “standing next in order” Ex: Germanium (Ge) was predicted by Mendeleev, called ekasilicon Able to predict both physical and chemical properties via: *Some element properties can be found by averaging the respective properties of elements just above or just below an element in the PT* Example Pg. 126 Given: Density of Si = 2.3 g/cm3, Sn = 7.3 g/cm3 Estimate the density of Germanium. Where are Si, Sn and Ge located on the Periodic Table? To Solve – average the two known densities together. ( .

/

.

/

)

Estimated density of Ge

We can also use this for melting point/boiling point estimates! ---Writing Binary Ionic Compounds --We’ll get to that! First… A12 – What determines properties? Key points:

-Read section aloud-

The Physical and Chemical properties of an element are governed by the number and arrangement of the atom’s electrons. The electrons in the outer shell are most important! 1, 2, t-t-t-t-t-t-t, 3, 4, 5, 6, 7, 8

The charges on the columns are…. +1, +2, +2222222, +3, +/-4, -3, -2, -1, 0 You should write this on your own PT… Metals have stronger attractions between atoms than nonmetals  therefore they have higher melting points than nonmetals Writing Binary Ionic Compounds 1) If the charges are the same, they cancel Examples: Na+ and Cl2) If the charges are different, “criss-cross” Examples: Mg+2 and Cl-

Time to do some practice… Answer the questions on page 126

When finished, check your answers 1) – 149 °C 2) a.320 K b. sodium higher 3) GeCl4 4) a. CF4 b. Al2S3 c. KCl d. CaBr2

e. SrO