Chemistry Ch. 4

a measure of how close a

measurement comes to the accepted or

true value of whatever is measured

Accuracy

is a measure of how close a series of measurements are to one another, irrespective of the accepted value.

precision

______________ Requires two or more repeated

measurements

precision

Darts on a dartboard illustrate the difference

between ___________ and __________

accuracy and precision

The closeness of a dart to the bull's-eye corresponds to

the degree of __________. The closeness of several darts to

one another corresponds to the degree of _____________.

accuracy

precision

the correct value for the

measurement based on reliable references

accepted value (exact; true)

value measured in the lab

experimental Value

What is the equation for calculation % error?

I experimental - accepted I

% error = ---------------------------- x 100

accepted value

Measuring precision requires ____ or more

measured data points

2

What are the data points that measuring precision requires?

- Find the average of the

readings

- Determine the highest

measured value.

-Find the lowest measured

value

- Subtract the lowest value

from the highest.

- Report the range as the

precision

Sometimes you have bad data and the

_________ comes close to the _________ number. You

must look at the __________ so see how large of

swing there is.

average

accurate

precision

No, measurements are precise if they are easily

____________, but not accurate if they do not

reflect the ________ ______.

reproducible

accepted value

Who created the word atomos meaning atom?

domocratis

The number of protons in the nucleus of the atom.

atomic number

Usually from a Greek or

Latin word for the element or a substance containing the element.

element name

The average mass of the atoms in an element.

* Round this off to get the mass number

Atomic mass

Short-hand abbreviation for the element name.

symbol

What make up the nucleus?

protons and neutrons

________ and __________ are held together by a strong force.

protons and neutrons

The total number of

protons and neutrons in an atom (protons + neutrons)

mass number

The total number of

protons in an atom. (______ = protons)

atomic number

What makes one element different from another?

Elements are different because they contain different

numbers of protons (atomic number)

Atomic Number (periodic table) = _________

• # protons = __________ (if a neutral atom)

____________ = Atomic Number (protons) + Neutrons

• Neutrons = ________________________________

# protons

# electrons

Mass Number

Mass Number

Mass number - Atomic number

What makes an atom an ion?

if it looses or gains electrons and Electrons are not equal to the protons

What is a cation?

an atom with a positive charge (lost electrons):protons > electrons

what is an anion?

an atom with a negative charge (gain electrons):protons < electrons

atoms of the same

element that have equal

protons but different

numbers of neutrons

isotopes

If isotopes have the same protons, then they have the same _____________ number, but different ____________ number

atomic

mass

What is carbon 14 used for?

carbon dating

Isotopic signatures are commonly known as

______________, because they are similar to human

______________ and are used to track and trace.

- They are found in water, land, plants and

animals

fingerprints

fingerprints

All elements have ____________.

isotopes

What are the 2 main types of isotopes?

Stable and unstable

isotopes that are non-radioactive forms of atoms.

stable

Radioisotopes are the unstable forms of an element

that emit radiation (called radioactive).

• Unstable:

Atoms with an unstable nucleus regain

stability by shedding excess particles and energy in the

form of radiation. They "want" to give up some energy

radioactive

Radiation is emitted by _______ ________ or ___________

alpha (a), beta (b) or gamma (g).

of the 118 elements listed in the periodic table, only ___ occur naturally

94

The weighted average

mass of all isotopes in a

naturally occurring

sample of the element

atomic mass