Basics of Matter and Half-Life

Matter

Anything that has mass and takes up space

e.g. Log in fireplace

seems like law or matter got destroyed, but the ash that’s leftover, it has less mass because it weighs less.

The matter didn’t get destroyed, is the rest of that bonded with oxygen when it was burning and now it’s now gaseous.

So the rest of its spread out

Law of Conservation of Matter

states that matter cannot be created or destroyed; it simply changes forms

Elements

A substance that cannot be separated into simpler substances by chemical means.

e.g. hydrogen, helium, iron, barium, mercury.

Atom

the smallest unit of an element that still has the properties of that element.

e.g. if you have one atom of hydrogen it’s still going to want to react and bond and behave in exactly the same way as if you had a whole canister of hydrogen

An ___ has all those same properties as a bunch of these atoms. Hence, that smallest unit of that unit

Atoms are composed of three basic SUBATOMIC PARTICLES

Protons- positive charge

Neutrons- neutral charge

Electrons- negative charge

Protons

Positive Charge

Located in Nucleus

Mass is 1 AMU

Neutron

• Neutral charge

• Located in nucleus

• Mass is 1 AMU

Electron

• Negative charge

• Orbits outside the nucleus

• Mass is 1/1836 AMU

(so tiny, you can round it off to the nearest whole. number)

Atomic Mass (AMU)

The amount of matter that makes up an atom.

AMU can be estimated by adding up its total number of protons and neutrons.

one-twelfth the mass of a carbon-12 atom

e.g., if you have a typical helium atom that has (2) two protons and (2) two neutrons, then it would be 4 AMUs

Balanced Atom

THE ONES WITH THE SAME NUMBER OF PROTONS AND ELECTRONS = NEUTRAL

same number of protons and electrons

one positive for every negative, those two sort of cancel each other out, and you end up with a neutral

if you have more electrons than protons, the overall charge is negative

Atom with an imbalanced charge is called an

ion

THE ONES WITH A POSITIVE OR NEGATIVE CHARGE

• atom that has gained or lost electrons, giving it a net electric charge

when you have more or less protons than electrons, you end up with a positive or negative charge

we call the particles that have a positive or negative charge, we call those atoms ions

so an ion either has more electrons than protons OR fewer electrons than protons

You can change the number of ____ in an atom

Neutrons

• This won’t affect the charge, however, because neutrons are neutral in terms of charge,

• but neutrons do have mass, about 1 AMU per neutron

so when you CHANGE the number of neutrons, it changes the MASS of the atom

An atom with a different number of neutrons (but same protons) than its normal base number is called an

Isotope

Ion- smaller charge, smaller word

Isotope- bigger word, but neutral

this was a hint to remember

Atomic Number

the number of protons a particular type of atom has. The atomic number defines the type of element.

You can change the number of electrons and have an ion. and you can change the number of neutrons and have an isotope, but if you change the number of protons you have a whole new element.

e.g.

• Add a proton to helium, now you don’t have helium anymore, you have lithium.

• You take a proton away from helium, you no longer have helium, you have hydrogen

YOU CAN CHANGE ELECTRONS AND NEUTRONS AND STILL HAVE A HELIUM ION OR ISOTOPE

BUT IF YOU CHANGE THE NUMBER OF PROTONS, YOU HAVE A WHOLE NEW ELEMENT

Radioactive Decay and Half Life

most isotopes decay back to their “normal” forms over time.

the time required for half the atoms of a particular substance to disintegrate is known as that substance’s HALF LIFE.

What is the half life of C14 (carbon 14; carbon isotope)?

about 5,400 years

then after it starts turning into C12,

then the rate goes slooowwweeer over time.

because started with a lot more decaying in that first 5,400 years than in the next but it’s always within that period of time, half of what’s left decays back into its normal state and that’s why we have the term half-life

Carbon 14 (C12)

created in the earth’s atmosphere by cosmic rays.

• All living things absorb _____.

• When they die, this absorption stops and the organism’s existing C14 begins to radioactively decay back into C12.

Counting Rings on a Tree

• By analyzing the amount of C14 remaining in a dead organism,

• and comparing that quantity to the isotope’s known half life,

• scientists can determine how long ago the organism died.

c14 vs. c12, how much c14 is decayed back in each of those years? And then they can sample a human body, for example and they can say how much of that has decayed back

e.g. they can say this caveman lived 300,000 ago

or forensic scientist can say “this person must’ve been killed two months ago because this amount of C14 has decayed back into C12.

Specific How Long Ago Something Died and Why Question

Carbon14 dating stops working after a certain period of time. Things that are more than 50,000 years old, cannot be carbon-dated.

Reason: That’s about how long it takes for all the C14 to decay back into C12.

• this means that once it’s all C12, THERE’S NO RATIO TO COMPARE

• We can’t tell if it died 50,000 years and one day ago or 200,000 years ago because now it’s all C12.

• No more ratio, so the validity of this dating technique only goes back 50,000 years

But what about the dinosaurs?

• Many other elements have much longer half lives than C14. half-lives

• So the half-life of C14 is relatively short compared to some other things

How we date things over 50,000 years old: Many other elements have much longer half lives than C14. Every compound has its own unique half-life.

Think: dinosaurs or uranium

• Uranium and different rocks have much longer half-lives.

• We can look at how long those have been decaying and we can again trace time and look at

  • where things are buried in the sedimentary strata and what rocks are near them, date the rocks, and then imply from that the time when that animal died and got deposited in that rock layer