9/29 – Warm Up #2What are the subatomic particles found in the

nucleus? With this information, predict the charge of the nucleus.

The mass of silver in a beaker is 35.0 grams. When the silver is dropped into the beaker, the volume of the water changes. If the water level was initially at 25.0 mL, calculate the final volume of water, in mL.

Fill in the blanks: “Opposites ______ (attract/repel), while like charges _______ (attract/repel).”

9/30 – Warm Up #3In the early 1900’s, Ernest Rutherford performed an

experiment where he shot a POSITIVELY-CHARGED beam of radiation at a piece of gold foil.

First of all, remember that opposite charges ______ and like charges _____.

Most of the time, the beam of radiation went THROUGH the foil. This means most of the foil had a ________ charge. What part of the atom is this?

On rare occasions, the beam of radiation got DEFLECTED when it hit the foil. This means some of the foil had a _____ charge. What part of the atom is this?

Chapter 4.2-4.4The Nucleus, Atomic Mass and Isotopes

Remember:Nucleus = protons and

neutrons (POSITIVELY CHARGED)

DENSE – a lot of matter in a small space

A VERY small portion of the atom (mostly empty space)

Also Keep in Mind…Charges = positive,

negative, neutral

Like charges REPELPositive repels PositiveNegative repels Negative

Opposite charges ATTRACTPositive attracts NegativeNegative attracts Positive

Ernest Rutherford (1871-1937)

Discovered nucleus

Before him: atoms = positively charged blobs with some negative charged particles in it

Experiment: shot laser w/positive charged particles into gold foil

What Rutherford Found…Most particles go

through gold foilBUTSome particles deflected

MEANINGMost of gold foil =

negative-charged (electrons)

Small positive charged center (NUCLEUS)

Nucleus ContinuedOn Periodic Table:

Atomic Number – Number of PROTONS an atom has

STAYS CONSTANT (ALWAYS)

Element

Symbol

Isotopes!Isotopes – The same

element, but different numbers of neutronsDifferent FORMS of the

elementCarbon 12 (mass # =

12)

Ex. CarbonCarbon-12 (6p, 6n)Carbon-13 (6p, 7n)Carbon-14 (6p, 8n)

(radioactive)

To Find Atomic Mass…Take ALL forms of

element in universe, and find AVERAGE

Ex. CarbonAtomic Mass: 12.01

gramsA LOT of carbon-12

Small amount of carbon-13 and 14 Carbon-12

Shorthand Notation

C

12

6

Mass # - # of protons +

neutrons

Atomic# - # of protons

Nucleus ContinuedOn Periodic Table:

Average Mass – avg. mass of all isotopes of the atomIn gramsAlso called MOLAR MASS

Protons and NeutronsProtons do not

always equal neutrons

Ex. AluminumAtomic # 13 (13

protons)Mass: 26.98g (13

protons + 14 neutrons)

Why does this occur?

Aluminum

Warm Up #4For an element, which number will stay the same

and which number can be different? (atomic number or mass number). Explain why.

Why is the bottom number on the periodic table the AVERAGE atomic mass? Use “isotope” in your answer.

Write the correct short-hand notation of Carbon-13 (include mass number and atomic number)

If an element has an atomic number of 30, and a mass number of 65, how many neutrons does it have?