Launch: 9/173. Which of the following is true for isotopes?

a. they change the identity of an atom to a different element

b. they have varying atomic numbers

c. they have varying atomic masses

d. they have varying numbers of electrons

5. On the periodic table, why is Co (Cobalt) placed before Ni (Nickel) even though Ni has a lower atomic mass?a. Nickel has one more proton

b. Cobalt has fewer electrons

c. Nickel has a few more electrons

d. Cobalt has a lower density

Launch: 9/173. Which of the following is true for isotopes?

a. they change the identity of an atom to a different element

b. they have varying atomic numbers

c. they have varying atomic masses

d. they have varying numbers of electrons

4. Why are atomic masses listed as decimals on the periodic table instead of whole numbers?a. they are a weighted average of the naturally occurring

isotopes

b. their units are grams/moles

c. they were measured with a balance that read to only two decimal places

d. none of the above

How many electrons?Mr. HeffnerChemistry

9/17/09

What is atomic # and mass?

Atomic number = # of protons

Atomic mass = # protons + neutrons

Atomic mass – atomic number = # of neutrons

How many electrons?In a neutral atom,

The # of electrons = # of protonsThe # of electrons = atomic number

How many electrons?

1

HHydrogen

Atomic number

How many electrons?

79A

uGold

Atomic number

How many electrons?Not all atoms are neutral!

An ion is…a charged atom with an unequal number of

protons and electrons

Two types of ionsNegatively-chargedPositively-charged

How many electrons?Negatively charged ion

More “–” than “+”Gained electronExample: F–

9 protons10 electrons9 + (–10) = –1

How many electrons?Positively-charged ion

Less “–” than “+”Lost electronsExample: F+

9 protons8 electrons9 + (–8) = +1

SummaryFor an atom of a specific element

Things that can be different# of neutrons = isotopes# of electrons = ions

Things that must be the same# of protons!

Practice Questions1. What two things must be equal in a neutral atom?

2. How many electrons does a neutral atom of N have? What about S, Ne, and Ca?

3. Does a negatively charged ion have more protons or more electrons?

4. How many electrons does Na+ have? What about Mg2+, S2–, and P3–?

5. Fill in the following table.Element # Protons # Neutrons # Electrons

C

Cl

O2–

Oxygen-18

Exit Slip1. In a neutral atom, the number of protons is

equal to thea. number of neutrons

b. number of electrons

c. number of isotopes

d. charge on the ion

Exit Slip2. Which of the following is the correct definition

of an ion?a. an atom with at least three different isotopes

b. an atom that has they same number of electrons as it’s atomic number

c. an uncharged atom that has an equal number of protons and neutrons

d. a charged atom that has an unequal number of protons and electrons

Exit Slip3. Which of the following is true for an isotope?

a. it is not considered an element

b. it can have a variety of atomic numbers

c. it can have a variety of atomic masses

d. it can have a different number of protons than an atom of the same element

4. A neutral atom that has 15 electrons could bea. P (Phosphorus).

b. O (Oxygen).

c. N (Nitrogen).

d. K (Potassium).

Exit Slip5. Which of the following correctly lists the

number of protons, neutrons, and electrons in the negatively charged ion Cl–?a. 17 protons, 18 neutrons, 17 electrons

b. 17 protons, 18 neutrons, 18 electrons

c. 17 protons, 17 neutrons, 17 electrons

d. 17 protons, 17 neutrons, 18 electrons

HomeworkFinish practice questions

Pg. 86 Practice: #1

Pg. 89 Practice: #1

Pg. 107-108 Chapter Review: #5, 16, 30, 32, 33, 35