AP CHEM UNIT 1 VOCAB

compound

Atoms from different elements combined like, H20 = water.

mixture

Stuff mixed together Physically not chemically, can be seperated like sand & water.

molecule

2 or more atoms stuck together like 2 oxygen atoms.

Ion

An atom or molecule that has a charge (+/-) from gaining or losing electrons.

Cation

positive ion (lost electrons) PAWsitive

Anion

negative ion (gained electrons)

Isotope

Same atom (element) but with different # of neutrons. (Think of twin siblings who weigh differently).

Atomic Number

Number of Protons in the atom (tells us which element it is on the Periodic table).

mass number

Protons + neutrons, tells us how much "stuff" is in the Nucleus.

Homogeneous Mixture (solution)

Same throughout (like salt water or silver)

Heterogeneous Mixture

Different throughout can be seen and separated like a salad, or orange juice.

Sig Figs

Important Digits that represent Precision. (Accuracy)

Conservation of mass

matter can’t be destroyed or created

definite proportions

a compound always has the same ratio of elements

multiple proportions

elements can combine in different ratios to form different compounds (CO vs. CO2

Empirical formula

simplest whole number ratio of atoms

molecular formula

actual # of each atom

effective nuclear charge (Z_eff)

more protons means there’s a stronger pull on electrons

shielding

inner electrons block the nucleus’s pull on outer electrons especially when shells increase going down a periodic table

distance

more shells means the valence electrons are farther from the nucleus meaning there’s weaker attraction

atomic radius

LEFT → RIGHT: it decreases because of coulomb’s law (reason is because there is more protons going left to right meaning the proton pull is stronger)

TOP → BOTTOM: it increases because of electron shells being added meaning the size of the atom would be bigger, and easier to remove electrons)

ionization energy

LEFT → RIGHT: it increases because atoms hold the electrons tighter to the nucleus because of protons

TOP → BOTTOM: it decreases because the outer electrons are farther and easier to remove.

electronegativity

LEFT → RIGHT: it increases because nucleus attracts electrons more strongly

TOP → BOTTOM: it decreases because the distance and shielding reduces the attraction

Does a pure substance always have the same composition? Explain your reasoning.

yes, they contain only a single type of atom or molecule.

Does a mixture always have the same composition? Explain your reasoning.

No, They contain several different atoms/molecules, salt water for example, could have different compositions.

17. Will the number of electrons in an atom be greater than, less than, or equal to the number of protons in the atom

It would be the same, they have a net charge of zero.

Will the number of electrons in a cation be greater than, less than, or equal to the number of protons in the cation?

They will be less than

Will the number of electrons in an anion be greater than, less than, or equal to the number of protons in the anion?

They will be greater than.

25. Using the concept of effective nuclear charge, explain why the size of the atom generally decreases when going from left to right across the periodic table.

As you move from left to right across a period, the atomic size decreases because the number of protons in the nucleus increases, leading to a stronger effective nuclear charge (

Zeff

𝑍𝑒𝑓𝑓

). This stronger positive charge pulls the electrons in the same outermost shell closer to the nucleus, resulting in a smaller atomic radius.

Using the concept of electron shells, explain why the size of the atom increases when going from top to bottom of the periodic table.

As you move down a group in the periodic table, the atomic size increases because each new period adds a new electron shell, placing the outermost electrons farther from the nucleus.

Explain why a cation is smaller than the atom it comes from.

A cation removes one or more electrons, leaving the Nucleus to have a greater force, due to closer Pull.

Explain why an anion is larger than the atom it comes from.

An anion adds one or more elections, making the Nucleus have a weaker force between them due to excess space.

What is ionization energy?

The amount of energy needed to remove an electron from an atom/ molecute.

Explain how Coulomb's law can help explain ionization energy.

states that the force of attraction between opposite charges is:

• Stronger when the charges are larger.

• Weaker when the distance between the charges is greater. 

percent composition formula

mass of what you’re trying to find/mass of the whole thing x 100 = percent comp

empirical formula

take the numbers given, divided by atomic mass, then take the smallest # and divide them by all.