Atomic Structure 2

What is an isotope

Atoms with same number of protons but different number of neutrons

What do isotopes have the same of

Chemical properties

Why do isotopes have similar chemical properties

Same number of electrons

What is relative isotopic mass

Mass of one atom relative to 1/12 of carbon-12

What is relative atomic mass RAM

Weighted average mass of isotopes of an element

What determines RAM

Isotopic masses and their abundances

Why is RAM not a whole number

Because it is an average

What is relative molecular mass RMM

Sum of relative atomic masses in a molecule

What is relative formula mass

Sum of atomic masses in a formula unit

What instrument is used to find isotopes

Mass spectrometer

Step 1 of mass spectrometry

Vaporization of sample

Step 2 of mass spectrometry

Ionization by electron gun

Step 3 of mass spectrometry

Acceleration by electric field

Step 4 of mass spectrometry

Deflection by magnetic field

Step 5 of mass spectrometry

Detection of ions

What happens during vaporization

Sample is turned into gas

What happens during ionization

Electrons removed to form positive ions

What happens during acceleration

Ions gain kinetic energy

What happens during deflection

Ions separated based on mass to charge ratio

What determines degree of deflection

Mass and charge of ion

Heavier ions deflect more or less

Less

Lighter ions deflect more or less

More

What is m over e

Mass to charge ratio

What does a mass spectrum show

Relative abundance vs m/e

What is relative abundance

Percentage of each isotope

Example isotopes of chlorine

Cl-35 and Cl-37

Abundance of Cl-35

75 percent

Abundance of Cl-37

25 percent

RAM of chlorine calculation

35×0.75 + 37×0.25 = 35.5

What does peak height represent

Relative abundance

What does peak position represent

m/e ratio

Why do isotopes form multiple peaks

Different masses

What is the formula for RAM

Sum of isotope mass × abundance divided by 100

What is a molecule

A group of atoms bonded together

What is a formula unit

Empirical formula for ionic compound

What is an isoelectronic species

Species with same number of electrons

Example of isoelectronic species

F- and Na+

What is isotonic species

Atoms with same number of neutrons

Example of isotonic species

Na and Mg with same neutrons

What happens if protons equal electrons

Atom is neutral

What happens if protons greater than electrons

Atom is positive ion

What happens if electrons greater than protons

Atom is negative ion

What affects deflection in electric field

Charge and mass

Positive particles deflect toward

Negative plate

Negative particles deflect toward

Positive plate

Neutral particles deflect

Not deflected

What affects radius of deflection

Mass and charge

What affects angle of deflection

Charge and mass

Which has greater angle electron or proton

Electron

Which has greater radius proton or electron

Proton

Why electrons deflect more

Lower mass

Why protons deflect less

Greater mass

What is the purpose of mass spectrometry

Determine isotopic composition

What can be calculated from mass spectrum

Relative atomic mass

What is abundance percentage

Fraction of atoms of each isotope

How to convert percentage to fraction

Divide by 100

What is average mass

Weighted mean of isotopes

Why is carbon-12 standard

Used as reference for atomic mass

What does 1 amu represent

1/12 mass of carbon-12

What is atomic mass unit

Unit of atomic mass

What is the significance of isotopes

Explain fractional atomic masses

Why are isotopes important in chemistry

They affect atomic mass but not chemistry

What is a peak in spectrum

A signal for an isotope

What is the tallest peak

Most abundant isotope

What is fragmentation

Breaking of molecules into smaller ions

What type of ions detected

Positive ions

What happens if ion has higher charge

Lower m/e value

Why do ions need to be charged

To be accelerated and deflected

What is detection step

Recording ions hitting detector

What does detector measure

Current produced by ions

How is abundance measured

Intensity of signal

What is calibration in spectrometry

Adjusting instrument accuracy

What is resolution

Ability to distinguish close masses

What is precision

Consistency of measurements

What is accuracy

Closeness to true value

Example calculation of RAM

Cu isotopes weighted average

Example calculation of RAM

Mg isotopes weighted average

Why do heavier elements have more isotopes

More neutrons for stability

What is nuclear stability

Balance between protons and neutrons

What is neutron to proton ratio

N/P ratio

Typical N/P ratio for small atoms

About 1

Typical N/P ratio for large atoms

Up to 1.5

Why does N/P ratio increase

To counter proton repulsion

What happens if N/P ratio too high

Neutron rich unstable

What happens if N/P ratio too low

Proton rich unstable

How do unstable atoms become stable

Radioactive decay