Atomic Structure, Isotopes, and Atomic Mass

Flashcards covering electron charge and position, AMU definitions, atomic number and mass number, isotopes, ions, and how atomic mass is calculated.

Where are electrons located in an atom and what is their relative charge?

Outside the nucleus; electrons are negatively charged.

What unit is used to express atomic masses, and how is it defined?

The atomic mass unit (AMU); defined as 1/12 the mass of a carbon-12 atom.

What is the approximate mass relationship among protons, neutrons, and electrons in AMU?

Protons and neutrons are about 1 AMU each; electrons are about 1/2000 AMU.

What is the atomic number and what does it determine?

The number of protons in an atom; it determines the element.

In isotope notation, what does Z represent and where is it placed?

Z is the atomic number (number of protons) and is shown in the lower left of the symbol.

In isotope notation, what does A represent and where is it placed?

A is the mass number (sum of protons and neutrons) and is shown in the upper left of the symbol.

What does the upper-right number in isotope notation signify?

The ionic charge of the ion.

What is an isotope and what stays the same across isotopes of an element?

Isotopes have the same number of protons (same Z) but different numbers of neutrons; they share the same chemical properties.

How is the mass number defined in relation to protons and neutrons?

Mass number A = number of protons + number of neutrons (A = Z + N).

What is atomic mass and how is it determined?

Atomic mass is the decimal, weighted average of the isotopes of an element based on their natural abundances.

How is the weighted average atomic mass calculated from isotopic masses and abundances?

Atomic mass = sum over isotopes of (fractional abundance × isotope mass).

What are cations and anions, with examples?

Cations are positively charged ions (e.g., Li+, Ca2+); anions are negatively charged ions (e.g., F−, O2−).

How do you form a cation or anion from a neutral atom?

Cation forms by losing electrons; anion forms by gaining electrons.

How do you determine the ionic charge from the number of protons and electrons?

Charge = number of protons − number of electrons (positive if more protons, negative if more electrons).

What is the mass number of an isotope and how does it differ from atomic mass?

Mass number is an integer (protons + neutrons); atomic mass is a decimal weighted average of isotopes.

What is the mass of carbon-12 in AMU and in grams?

Carbon-12 has a mass of exactly 12 AMU; 1 AMU ≈ 1.66 × 10^-24 g.

How do you compute the atomic mass from isotopic masses and their abundances?

Use the formula: atomic mass = Σ (fractional abundance × isotope mass) for all isotopes.

What is isotope notation for copper-63 and copper-65 in terms of mass and abundance reasoning?

Isotopes Cu-63 and Cu-65 have the same number of protons (30) but different neutrons; their masses are weighted by natural abundances to give the element’s atomic mass.

What is the difference between the two common isotope notations mentioned in the notes?

One style writes A and Z around the symbol (A on top left, Z on bottom left, charge on top right); the other style is X-A (element symbol followed by dash and mass number).