Day 13: Combining Metallic Atoms 7.1, 7.3Name ______
1)Atoms of metallic elements combine to form metallic solids held together by bonds that are quite different from the molecular bands of last class. Each atom has a few valence electrons. They are very loosely held. If these electrons were lost, then the electron structure would match that of a noble gas.
a)What noble gas is each of these metals closest to? How many electrons would they need to lose?
Li 1, HeCa 2, ArAl3, NeMg 2, Ne
b)In a metallic solid, the valence electrons are not attached to any particular nucleus. It is like a regular array of positive ions surrounded by a negative electron sea. This is similar to
A)Magnetic marblesB) LegoC) molecular kitD) all three
A)The magnetic marbles tend to form regular patterns, but they can be shifted into other shapes including lines, which is like metal wires.
c)How can this explain why metals are conductive?
Electrons are free to move through the solid. This can transfer charge or kinetic energy.
d)How can this explain why metals are malleable?
Electrons are free to move to hold ions together in any regular arrangement.
e)When metals of different elements combine, they form alloys which are considered homogenous mixtures (solutions) and not pure substances. Why?
They can mix in almost any ratio. You can show this with the pink and purple magnetic marbles.
2)Metallic elements can combine with non-metallic elements to form ioniccompounds. The metallic atoms lose their outer electrons and the non-metallic atoms gain them.
a)Draw a Bohr-Rutherford diagram of a sodium atom and a chlorine atom. Show where the electrons move with arrows.
b)The atoms now have opposite charges and attract each other. The ions move so that each ion is surrounded opposite charges. You will be assigned either a positive or a negative charge. Move so that you have four opposite charges around you. Draw a diagram of what this looked like.
Give each student a card with a large positive or negative sign.
c)Your model was only 2-D. Make a 3-D version.
Provide them with different coloured spheres and skewers and have them make a 3-D version.
d)Look at some ionic compounds and some molecular compounds with a magnifying glass. Which of these form crystals?
Provide salt, flour, wax, icing sugar etc. (Granulated sugar is molecular and does form crystals, so you might want to leave it out.)
e)Ionic compounds form crystals, with sharp edges and flat faces at regular angles. Explain why.
The macroscopic structure comes from the aligning of the ions in a large array.
f)Ionic compounds do not conduct. Why?
The electrons are held tightly in place by the ions.
g)Ionic compounds are very brittle. Why?
If the structure is shifted slightly – positive ions will be next to positive ions and repel.
h)Ionic compounds do not conduct electricity, but do when they are dissolved in water.Explainhow this is possible with a diagram showing the solution, a battery and two electrodes.PhET
Test some of the solids that were examined for a crystal structure. The structure must break apart in water. The positive ions flow one way and the negatives the other.
3)We have examined three types of compounds.
a)Which type of compound will have the lowest melting point?
A)molecularB) metallic C) ionic
A) All three bond types are strong, but the molecular bond just holds an individual molecule together – not the macroscopic solid. The metallic bond can be really strong (transition metals) or moderate (alkali Earth metals, mercury, gallium).Model with small wooden molecules shaken in a large container vs. magnetic marbles and Lego
b)Which type of compound will be hardest?
A)molecularB) metallic C) ionicD) two of these
C) In general molecular compounds will be softest – with metals varying as discussed above.
c)Which type of compounds can make strong wires?
A) molecularB) metallic C) ionicD) two of these
B) Ionic compounds form 3-D structures – not 1-D. Metallic are easiest to form in strands. However, if you can make a long thing strand of molecular bonds they will be very strong as will be seen next class withcarbon fibres.
d)Which type of compound will form visible crystals?
A) molecularB) metallic C) ionicD) two of these
C) They are generally the largest and most visible. Metallic solids can also form crystalsbut tend to be too small to see unless cooled slowly. Some polar molecules like sugar also form crystals. Crystals are larger if they are grown slowly and without being jostled.This can be demosntarted with the magnetic marbles.
4) Examine the following pairs of elements. Which type of compound will they form?
A) ionicB) metallic C) molecular
Write the chemical formula for the compound.
a) Li, ClionicLiCl
b) C, OmolecularCO (and CO2)
c) Mg, OionicMgO
d) Fe, NimetallicNA
e) Al, OionicAl2 O3
f) H, OmolecularH2O (and H2O2)
g) Be, Brionic BeBr2
h) K, Oionic K2 O
Textbook Consolidation: Read pages 260-261, and answer question 6, 10, 11.
Time to do electroplating activity p. 242?