Major Concepts

Isotope Activity

•An element can have a different number of neutrons, but always has the same number of protons

•The atomic weight is the average weight of all the known isotopes of the element

•The element which appears on the periodic table is the isotope which is most abundant

Major Concepts cont.

Atomic Symbol

mass number

23 sodium-23

atomic number 11

• Elements of the same atom have the same atomic number, but different mass numbers

Na

3. Was it possible for an atom to make more than one bond? Explain, and give an example.

• All atoms except hydrogen can make more than one bond

• For example…….

Activity 17 Analysis

4. How many bonds could each of the following make with hydrogen?

a. Si (Atomic # 14) 4

b. S (Atomic # 34) 2

c. I (Atomic # 53) 1

d. As (Atomic # 33) 3

5. If you had two oxygen atoms and one hydrogen atom, could you form a molecule? Explain.

• No• With 2 oxygens bonded together, you could

bond 1 hydrogen. • One of the oxygen atoms would have an

unbonded site.• It is not possible to put them together with all

sites bondedH

O OUnbonded site

6. Make a drawing of the models to show the difference between an atom and a molecule.

• a molecule is made of more than one atom.• it can be the same atom or it can be

composed of more than one kind of atom.• example of each…….

H H

O

Molecule

Atom

Name _______________ Period ____ Date _______

Activity 17, Analysis # 6 & Activity 16, Analysis #4

Demo: Sodium in WaterChemical Formula2Na(s) + 2H2O(l) ------ 2NaOH(aq) + H2(g)

Sodium and hydrogen are both in group 1 and are very reactive. When the sodium reacts with the water it takes the place of one of the hydrogen atoms. This happens because sodium is more reactive than the hydrogen it is replacing. Reactivity is largely due to the atomic radius of an element and the valence. Larger metals lose their outer electrons more easily. If the sodium was less reactive than the hydrogen then there probably would be no chemical reaction in this case.