Chemistry: Electrons, Models & Energy Levels

Why do scientists use models of the atom?

atoms are too small to see so models help us picture and predict their behaviour

Why is no atomic model perfect?

every model trades some accuracy for simplicity or usability

What is the electron cloud model also called?

the quantum mechanical or Schrodinger model

What does the electron cloud model show?

a fuzzy cloud of where electrons are likely to be (darker means more likely)

What is a strength of the electron cloud model?

it captures the wave nature of electrons and the tiny nucleus in a large cloud

What is a limitation of the electron cloud model?

it does not show particle nature so you cannot count the electrons

What does the Bohr model show?

electrons as dots on rings around a small nucleus

What is a strength of the Bohr model?

it shows electrons as countable particles and shows their energy levels

What is a limitation of the Bohr model?

it hides the wave nature and wrongly implies fixed positions and paths

What is the difference between the Bohr and electron cloud models?

Bohr shows electrons as particles on rings while the electron cloud shows a fuzzy probability cloud

What do the rings in a Bohr model represent?

the discrete energy levels or shells electrons can occupy

Do electrons orbit the nucleus like planets?

no the rings only represent energy levels not real paths

What does it mean that energy levels are quantized?

electrons can only have specific energies not values in between

What is a good analogy for quantized energy levels?

rungs of a ladder since you can stand on a rung but not between them

How many electrons can the first shell hold?

2

How many electrons can the second shell hold?

8

How many electrons can the third shell hold before the next begins?

8

What is the electron-filling pattern of the first three shells?

2 then 8 then 8

How does electron energy change with shell number?

the higher the shell number the greater the energy of its electrons

What is the ground state of an electron?

the lowest possible energy level it can occupy

How many electrons can a single orbital hold?

2

What is the valence shell?

the outermost shell of an atom

What are valence electrons?

the electrons in the outermost shell

What are core electrons?

any electrons that are not in the outermost shell

Why are valence electrons important?

they are most easily shared or transferred so they drive chemical reactions

An atom has its shells filled 2 then 8 then 7. How many valence electrons does it have?

7 (the outer shell)

What did the Bohr model successfully explain?

why atoms absorb and emit light at only certain wavelengths

Where did the Bohr model fail?

it could not predict the spectra of atoms with more than one electron

What did de Broglie propose about electrons?

that they also behave as waves forming standing-wave patterns around the nucleus

Why did de Broglie's wave idea explain the allowed energy levels?

only certain standing-wave patterns can fit around the atom

What did Schrodinger contribute?

a mathematical model giving the probability of where an electron is likely to be

What are orbitals?

regions around the nucleus where an electron is most likely to be found

How did the three main models build on each other?

Bohr quantized energy levels de Broglie added electron waves and Schrodinger unified them into the modern quantum model