Chemistry — Atoms, Ions, Isotopes & Atomic Mass

What are atoms?

the fundamental building blocks that make up all matter

What are the three subatomic particles in an atom?

protons neutrons and electrons

What is the charge of a proton?

positive (+1)

What is the charge of a neutron?

neutral (0)

What is the charge of an electron?

negative (-1)

Where are protons and neutrons found?

in the nucleus

Where are electrons found?

in the electron cloud around the nucleus

What is the nucleus?

the dense core of the atom that holds the protons and neutrons

What is the electron cloud?

the region around the nucleus where electrons are likely to be found

What does the number of protons determine?

the identity of the element

What determines how an atom bonds and reacts?

its electrons

Where is almost all of an atom's mass?

in the nucleus (its protons and neutrons)

Where is almost all of an atom's volume?

in the electron cloud

Why do electrons add almost no mass?

an electron is roughly 1/2000 the mass of a proton or neutron

What is the atomic number?

the number of protons in an atom

In a neutral atom what does the atomic number also equal?

the number of electrons

What makes an atom electrically neutral?

equal numbers of protons and electrons

What is an ion?

an atom or group of atoms with a net electric charge

How does an atom become an ion?

by gaining or losing electrons so protons and electrons no longer balance

During a chemical reaction what never changes in an atom?

the number of protons

In a reaction what actually moves between atoms?

electrons

When one atom loses electrons what happens to another atom?

it gains them so one becomes positive and the other becomes negative

Does gaining or losing electrons change which element it is?

no because only the number of protons defines the element

What is a cation?

a positive ion formed by losing electrons

What is an anion?

a negative ion formed by gaining electrons

How does an atom become a positive ion (cation)?

by losing electrons so it then has more protons than electrons

How does an atom become a negative ion (anion)?

by gaining electrons so it then has more electrons than protons

How is cation pronounced?

CAT-ion

How is anion pronounced?

AN-ion (not like onion)

How do you calculate an ion's charge?

subtract electrons from protons (a positive answer means a cation and a negative answer means an anion)

An atom has 11 protons and 10 electrons. What is its charge?

1 plus (11 minus 10)

An atom has 12 protons and 10 electrons. What is its charge?

2 plus (12 minus 10)

An atom has 13 protons and 10 electrons. What is its charge?

3 plus (13 minus 10)

An atom has 17 protons and 18 electrons. What is its charge?

1 minus (17 minus 18)

An atom has 20 protons and 18 electrons. What is its charge?

2 plus (20 minus 18)

An atom has 7 protons and 10 electrons. What is its charge?

3 minus (7 minus 10)

An atom has 78 protons and 74 electrons. What is its charge?

4 plus (78 minus 74)

How do you write an ion symbol?

the element symbol with a superscript charge (the number then a plus or minus sign)

What do you do with the number when an ion charge is 1 plus or 1 minus?

leave the 1 out (a 1 plus ion is written with just a plus sign)

How would you write an ion of element X with a 3 plus charge?

X3+ (the symbol then the number then a plus or minus sign as a superscript)

How is a cation named?

the same as the neutral element (for example a sodium ion)

How is an anion named?

the element name is changed to end in -ide

What ending signals a negative ion (anion)?

the -ide ending

What is the ion of chlorine called?

chloride

What is the ion of oxygen called?

oxide

What is the ion of nitrogen called?

nitride

What is a polyatomic ion?

a group of atoms bonded together that carries one net charge and acts as a single unit

What is the formula of hydroxide?

OH minus

What is the formula of nitrate?

NO3 minus

What is the formula of carbonate?

CO3 2 minus

What is the formula of sulfate?

SO4 2 minus

What is the formula of phosphate?

PO4 3 minus

What is the formula of ammonium?

NH4 plus

Why do ions matter in chemistry and biology?

they form ionic compounds conduct electricity in solution and drive things like batteries and nerve signalling

What is the mass number?

the total of protons plus neutrons (mass number = protons + neutrons)

How do you find the number of neutrons?

subtract the atomic number from the mass number

An atom has a mass number of 195 and 78 protons. How many neutrons does it have?

117 (195 minus 78)

What are isotopes?

atoms of the same element with different numbers of neutrons

What is identical across all isotopes of an element?

the number of protons (its atomic number and identity)

What varies between isotopes and changes their mass?

the number of neutrons

In isotope symbol notation what does A stand for?

the mass number (the top-left number)

In isotope symbol notation what does Z stand for?

the atomic number (the bottom-left number)

In isotope symbol notation what does X stand for?

the element's chemical symbol

In hyphen notation like carbon-13 what does the number mean?

it is the mass number

Carbon-12 and carbon-13 are examples of what?

isotopes (same element with different neutron numbers)

An isotope has 6 protons and a mass number of 12. How many neutrons?

6 (12 minus 6)

An isotope has 6 protons and a mass number of 13. How many neutrons?

7 (13 minus 6)

What is the unified atomic mass unit (u)?

the standard unit for the mass of atoms and subatomic particles

What is the mass of a proton and of a neutron in u?

each is about 1 u

What is average atomic mass?

the weighted average mass of an element's naturally occurring isotopes

Why is a periodic table mass not a whole number?

it is a weighted average across several isotopes

What are the isotope masses weighted by?

the natural abundance of each isotope

How do you calculate average atomic mass?

multiply each isotope mass by its fraction then add the results

How do you turn a percentage abundance into a fraction?

divide the percentage by 100

What is a quick check on your abundance fractions?

they should add up to 1 (100%)

Where does a weighted average always lie?

closest to the mass of the most abundant isotope

What is the average mass when 80% is 5 u and 20% is 6 u?

5.2 u

What is relative atomic mass?

the unitless average atomic mass listed on the periodic table

What is the older term for average atomic mass?

atomic weight (though it really means mass not weight)

What was Rutherford's contribution to atomic theory?

he discovered the nucleus

What was Bohr's contribution to atomic theory?

electrons occupy specific energy levels or orbits

What is the nickname of Thomson's model?

the plum pudding model

What are the five atomic models in order?

Dalton then Thomson then Rutherford then Bohr then Schrodinger

What is the modern model of the atom?

the electron cloud model (Schrodinger)