2.1.1 Atomic Structures and Isotopes

What are isotopes?

Atoms of the same element with different number of neutrons an different masses

Explain why isotopes of an element react in the same way

• isotopes have the same number of electrons in the outer shell

• chemical reactions involve electrons and neutrons make no difference to chemical reactivity of an element

How many isotopes is Hydrogen made of?

3

Give the name of the 3 Hydrogen isotopes

• Protium

• Deuterium

• Tritium

PNE of protium?

• P:1

• N:0

• E:1

PNE of deuterium?

• P:1

• N:1

• E:1

PNE of tritium?

• P:1

• N:2

• E:1

How many isotopes is carbon a mixture of?

3

PNE of C-12?

• P:6

• N:6

• E:6

PNE of C-13?

• P:6

• N:7

• E:6

PNE of C-14?

• P:6

• N:8

• E:6

Who first proposed the idea of an atom and when?

• Democritus

• 5th century BC

How did Democritus describe atoms?

• bits of matter too small to see

• they can not be split

• solid

• no internal structure

• different in size, shape and weight

Who created the billiard ball model of the atom and when?

• John Dalton

• Early 1800s

When was the plum pudding model?

• 1889

Who proposed the plum pudding model?

• J J Thompson

What was the plum pudding model?

negative electrons floating round in a positively charged atom to make a neutral atom

What experiment resulted in the conclusion atoms are not solid?

Alpha particle scattering experiment

Who carried out the alpha particle scattering experiment?

Rutherford

When did the alpha particle scattering experiment take place?

1909

Describe the alpha particle scattering experiment

• positively charged alpha particles fired at a thin sheet of gold leaf

• most bounced off, but some went straight through

Describe the conclusions made from the alpha particle scattering experiment

• atom have a nucleus which is very small and dense, and contains most of the atom’s mass and is positively charged

• atoms consist of mostly empty space

• electrons are attracted to the nucleus but stay mostly outside of it

What provided evidence for the existence of isotopes?

Radioactive decay

What causes radioactive decay?

• the nuclei of some isotope are unstable

• they can split or ‘decay’ releasing radiation

Who improved Rutherford’s model of the atom?

Niels Bohr

How did Bohr create the Bohr model of the atom?

• using information from the measurements of light emitted from hydrogen atoms

• mathematical moddeling

Describe the Bohr model of the atom

a nucleus with electrons orbiting at specific distances on shells

Who discovered the proton and when?

Ernest Rutherford

How did Dirac explain electrons?

they exist as a cloud of probability outside of the nucleus

What theory did Dirac use to get his electron theory?

Einstein’s theory of relativity

Following Dirac’s work, how is the atom depicted?

a mathematical probability and not a physical image

Who discovered the neutron and when?

• James Chadwick

• 1932

Name 3 subatomic particles

• protons

• neutrons

• electrons

Describe the relationship of protons and electrons in an atom

• the charge of protons and electrons is the same in magnitude but opposite in sign

• an ATOM must have the same number of protons as electrons

What is the charge of all atoms?

neutral

What is the mass and relative charge of:

• Protons?

• Neutrons?

• Electrons?

• Protons:

  • relative mass: 1

  • relative charge 1+

• Neutrons

  • relative mass: 1

  • relative charge: 0

• Electrons

  • relative mass: 1/1836

  • relative charge: 1-

What is common in all atoms of the same elements?

The number of protons

What holds electrons in place?

Attractive force from the nucleus

What does the atomic number represent?

number of protons in the nucleus of an atom

What does the mass number represent?

number of protons + neutrons in the nucleus of an atom

What happens when an atom loses x electrons?

it becomes an ion with the charge of x+ because it has x more protons than electrons

What happens when an atom gains x electrons?

it becomes an ion with the charge of x- because it has x more electrons than protons

Define relative isotopic mass

The mass of an atom compared to 1/12 of the mass of an atom of carbon-12

What is the relationship between relative isotopic mass and mass number for any isotope?

they will be the same

Define relative atomic mass

The weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12

What is the International standard for the measurement of isotopic and atomic masses?

the mass of a carbon-12 atom

What does ‘weighted mean mass’ take into account?

• the percentage abundance of each isotope

• the relative mass of each isotope

What place are RAM generally given to?

1 decimal place

What can mass spectrometry be used to determine?

• the relative abundances of all an elements isotopes

• the relative isotopic masses of each isotope

How do scientists calculate relative atomic masses?

• they use mass spectrometry to calculate it from the relative abundance of each isotope (and their relative isotopic masses)

Describe the process of mass spectrometry

• the sample is vaporised

• the sample is ionised to form positive ions

• the ions are accelerated

  • heavier ions move slower/ are less deflected

• The ions are detected as a mass-to-charge ratio, written as mz

  • Each ion produces a signal, so the larger the signal, the greater the abundance

What does relative molecular mass apply to?

Simple molecules covalently bonded with a fixed number of atoms in each molecule

What does relative formula mass apply to?

Compounds with giant structures which use an empirical formula

How are relative molecular masses and relative formula masses calculated?

• adding up the RAM of each atom in the molecule/ formula

Calculate the relative formula mass of ethanol (C2H5OH)

• 46

Calculate the relative molecular mass of CaCl2

• 111