Chem midterm

Calculate (2.3 x 10^-3)(-3.0 x 10^-2)

-6.9 x 10^-5

What is the net electric charge of this object? Note for advanced students: you can assume charge is measured in any convenient units, e.g. coulombs or units of e. Write down only the number part of your answer.

0

Write 7.977 x 10^-2 as a decimal

0.07977

A chemist needs to know the mass of a sample of CaCO3 to 3 significant digits. She puts the sample on a digital scale. This is what the scale shows: 0023.43 g If the measurement is precise enough for the chemist round it to 3 significant digits.

23.4 g

How many valence electrons are in a neutral atom of aluminum?

3

How many valence electrons are in Pb+?

3 (look at the group) if it has + take away one valence electron if it has a - add one valence electron

Write 0.004209 in scientific notation

4.209 x 10^-3

How many valence electrons are in Te-?

7

How many valence electrons are in a neutral atom of xenon (Xe).

8

The chemical formula for ammonium carbonate is (NH4)2CO3 How many hydrogen atoms are in each formula unit of ammonium carbonate

8

Write the chemical symbol for an element in Period 3 Group 3A

Al

How do you find valance electrons ?

Look at the group the element is in

What is a period on the periodic table?

horizontal row

What is a group on the periodic table?

vertical column

Write the symbol for every chemical element that has atomic number greater than 55 and atomic mass less than 140.6 u.

Ba, La, Ce

Write the chemical symbol for an element in Period 2 and Group 2A.

Be

Write the chemical formula for this molecule

C2H4O2

How many protons are in a neutral atom of calcium? How many electrons?

Number of protons = 20 Number of electrons = 20

How many protons are in a neutral atom of lanthanum (La)? How many electrons ?

Number of protons= 57 Number of electrons= 57

In what period is sodium? In what group?

Period= 3 Group= 1A

Write the chemical formula for this molecule

SOCl2