EL 3 Electrons, where would we be without them?

What are the subatomic particles in an atom?

Protons neutrons and electrons

What is the relative charge of a proton

neutron

What is the mass of a proton and neutron?

Approximately 1 atomic mass unit (amu)

What is the mass of an electron?

Approximately 1/1836 amu

Where are electrons located in an atom?

In orbitals around the nucleus.

What is the maximum number of electrons in the first shell?

2

What is the maximum number of electrons in the second and third shells?

8 electrons.

What is the Aufbau principle?

Electrons fill the lowest energy orbitals first.

What is Hund’s rule?

Electrons occupy orbitals singly before pairing up.

How is the electron configuration of sodium written?

1s² 2s² 2p⁶ 3s¹.

What is the electronic configuration of chlorine?

1s² 2s² 2p⁶ 3s² 3p⁵.

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How many orbitals does the s sub-shell have?

1

How many orbitals does the p sub-shell have?

3

How many orbitals does the d sub-shell have?

5

How many orbitals does the f sub-shell have?

7

How many electrons can fit in a single orbital?

2

What shape does an s-orbital have?

Spherical.

What shape does a p-orbital have?

Dumbbell-shaped.

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How does electronic configuration relate to the periodic table?

Periods indicate the number of electron shells

and groups indicate the number of outer-shell electrons.

What is the configuration of an atom in Group 2?

Ends in an s² orbital.

What is the configuration of an atom in Group 6?

Ends in a p⁴ orbital.

What causes the periodicity of elements?

Repeated patterns in their electronic structure.

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Who proposed the first atomic theory?

John Dalton.

What model did J.J. Thomson propose?

Plum pudding model.

What experiment did Rutherford use to refine the atomic model?

Gold foil experiment.

What was Niels Bohr’s contribution to atomic theory?

Electrons orbit the nucleus in fixed energy levels.

What is the quantum mechanical model?

Electrons are located in orbitals not fixed paths.

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What are the four stages of mass spectrometry?

Ionization

acceleration

deflection

detection.

What is ionization in mass spectrometry?

The process of removing one or more electrons to form a positive ion.

What is the purpose of acceleration in mass spectrometry?

To ensure ions have the same kinetic energy.

How are ions deflected in a mass spectrometer?

By a magnetic field depending on their mass-to-charge ratio (m/z).

What does the mass spectrum show?

The relative abundance of isotopes and their m/z ratio.

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What is spectroscopy?

The study of how substances absorb or emit electromagnetic radiation.

What is an absorption spectrum?

A spectrum with dark lines where light has been absorbed by a substance.

What is an emission spectrum?

A spectrum showing the wavelengths of light emitted by excited atoms.

What is the difference between absorption and emission spectra?

Absorption shows missing wavelengths

emission shows emitted wavelengths.

emission shows emitted wavelengths.

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**Write the electron configuration of phosphorus (Z=15).

** 1s² 2s² 2p⁶ 3s² 3p³.

**What is the electronic configuration of an atom with [Ar]3d⁵4s²?

** Manganese (Z=25).

**Describe how electrons are arranged in a 3p orbital.

** Three orbitals with one electron in each orbital before pairing.

**What is the mass-to-charge ratio (m/z) for an ion with a mass of 20 amu and a charge of +2?

** m/z = 10.

**How does the gold foil experiment show the nucleus exists?

** Most alpha particles passed through

**Why is the 4s orbital filled before the 3d orbital?

** The 4s orbital has a lower energy than the 3d orbital.

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**Why do d-block elements have complex configurations?

** Energy levels of 3d and 4s orbitals are close

**What is the significance of paired electron spins?

reduce repulsion and stabilize orbitals

**How does mass spectrometry help identify elements?

** By determining isotope abundance and m/z ratios.

**Why does the 3d orbital fill after the 4s orbital in elements like calcium?

** After filling

**What is the general rule for filling 3d and 4s orbitals?

** 4s orbital fills before 3d because 4s has slightly lower energy in isolated atoms.

**When are electrons removed from 3d and 4s orbitals in ions?

** Electrons are removed from the 4s orbital first because 4s becomes higher in energy than 3d after filling.

**Why does the 4s orbital fill before 3d in neutral atoms?

4s orbital has lower energy than 3d when empty

**Why does the 4s orbital lose electrons before the 3d orbital in ions?

** 3d orbital becomes lower in energy than 4s after electrons occupy the 3d subshell.

**What is special about chromium’s electron configuration?

** Chromium has the configuration [Ar] 3d⁵ 4s¹ because a half-filled 3d orbital is more stable than 3d⁴ 4s².

**What is special about copper’s electron configuration?

** Copper has the configuration [Ar] 3d¹⁰ 4s¹ because a fully filled 3d orbital is more stable than 3d⁹ 4s².

**Why do chromium and copper deviate from the Aufbau principle?

** They gain extra stability with half-filled (3d⁵) or fully filled (3d¹⁰) d-orbitals even though 4s loses one electron.

**How many electrons can the 3d and 4s orbitals hold?

** The 3d orbital can hold 10 electrons and the 4s orbital can hold 2 electrons.

**What is the general stability rule for d-orbitals?

** Half-filled (d⁵) and fully filled (d¹⁰) d-orbitals are more stable due to symmetrical electron distribution.

**What happens to 3d and 4s orbitals across a period?

** The 3d orbital fills after 4s but becomes lower in energy once electrons occupy it.