atomic structure, isotopes & electron configuration

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Who proposed the first modern atomic theory?

Dalton (1803) proposed that matter is made of tiny, indivisible atoms and that atoms of the same element are identical.

What were the main ideas of Dalton's atomic model?

Matter is made of atoms; atoms cannot be created or destroyed; atoms of the same element are identical; atoms combine in fixed ratios to form compounds.

Who discovered the electron?

J.J. Thomson (1897) discovered the electron through cathode ray tube experiments.

What was Thomson's atomic model?

The Plum Pudding Model: electrons embedded throughout a positively charged sphere.

Why was Thomson's model rejected?

It could not explain Rutherford's Gold Foil Experiment and did not include a nucleus.

What was Rutherford's Gold Foil Experiment?

Alpha particles were fired at thin gold foil; most passed through while a few were strongly deflected or bounced back.

What did Rutherford conclude from the Gold Foil Experiment?

Atoms are mostly empty space, with a small dense positively charged nucleus containing most of the atom's mass.

What contribution did Bohr make to atomic theory?

Bohr proposed that electrons exist in specific energy levels (electron shells) around the nucleus.

What contribution did Chadwick make to atomic theory?

Chadwick discovered the neutron in 1932.

Why was Chadwick's discovery important?

It explained why atoms of the same element can have different masses (isotopes).

What are the three subatomic particles?

Protons, neutrons and electrons.

What is the charge, mass and location of a proton?

Charge +1; relative mass 1; located in the nucleus.

What is the charge, mass and location of a neutron?

Charge 0; relative mass 1; located in the nucleus.

What is the charge, mass and location of an electron?

Charge -1; relative mass 1/1836 (approximately 0); located in electron shells around the nucleus.

What mnemonic can be used to remember particle charges?

PEN: Proton = Positive, Electron = Negative, Neutron = Neutral.

What is the atomic number?

The number of protons in an atom's nucleus.

Why is the atomic number important?

It identifies the element. Changing the number of protons changes the element.

What is the mass number?

The total number of protons and neutrons in the nucleus.

What is the formula for mass number?

Mass Number = Protons + Neutrons.

What is the formula for calculating neutrons?

Neutrons = Mass Number − Atomic Number.

How many neutrons are in Oxygen-16?

8 neutrons (16 − 8 = 8).

How many neutrons are in Sodium-23?

12 neutrons (23 − 11 = 12).

How many neutrons are in Magnesium-24?

12 neutrons (24 − 12 = 12).

What is an isotope?

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Why are Carbon-12 and Carbon-14 both carbon?

Both contain 6 protons, so they are the same element.

What differs between Carbon-12 and Carbon-14?

The number of neutrons. Carbon-12 has 6 neutrons; Carbon-14 has 8 neutrons.

Do isotopes have the same electron configuration?

Yes, isotopes of an element have the same number of electrons and therefore the same electron configuration.

Why do isotopes have similar chemical properties?

Chemical properties depend on electron configuration and valence electrons. Since isotopes have the same electron configuration, they have similar chemical properties.

Why do isotopes have different physical properties?

Isotopes have different numbers of neutrons and therefore different masses, affecting physical properties such as density and diffusion rate.

Which properties of isotopes are the same?

Number of protons, number of electrons, electron configuration, valence electrons and chemical properties.

Which properties of isotopes are different?

Number of neutrons, mass, density, some physical properties and radioactivity (for unstable isotopes).

Explain why isotopes have similar chemical properties but different physical properties.

Isotopes have the same number of electrons and therefore the same electron configuration and valence electrons, giving similar chemical properties. They have different numbers of neutrons, resulting in different masses and physical properties.

How do isotopes compare to the pure element?

Isotopes are still the same element because they have the same number of protons. They behave chemically like the element but may differ physically because of mass differences.

What is relative atomic mass (Ar)?

The weighted average mass of an element's naturally occurring isotopes compared to 1/12 of the mass of a carbon-12 atom.

Why is relative atomic mass often not a whole number?

It is a weighted average based on the abundance of different isotopes.

What is an electron configuration?

A representation of how electrons are arranged in energy levels (shells) around the nucleus.

How are electron shells filled?

Electrons occupy the lowest available energy level first before filling higher energy levels.

What is the electron configuration of Lithium?

2,1

What is the electron configuration of Oxygen?

2,6

What is the electron configuration of Sodium?

2,8,1

What is the electron configuration of Magnesium?

2,8,2

What is the electron configuration of Chlorine?

2,8,7

What is the electron configuration of Argon?

2,8,8

What are valence electrons?

The electrons in the outermost shell of an atom.

Why are valence electrons important?

They determine an atom's bonding behaviour and chemical reactivity.

How many valence electrons does sodium have?

1 valence electron.

How many valence electrons does magnesium have?

2 valence electrons.

How many valence electrons does chlorine have?

7 valence electrons.

How many valence electrons does neon have?

8 valence electrons.

Why do atoms form chemical bonds?

To achieve a more stable electron arrangement, usually a full outer shell.

What is the octet rule?

The tendency of atoms to gain, lose or share electrons to achieve eight electrons in their outer shell.

How can atoms achieve a full outer shell?

By gaining, losing or sharing electrons.

Which electrons are involved in bonding?

Valence electrons.

Who discovered the electron?

Thomson.

Who discovered the neutron?

Chadwick.

Whose experiment showed atoms are mostly empty space?

Rutherford.

Who proposed electrons occupy fixed energy levels?

Bohr.

What does atomic number tell you?

The number of protons in an atom.

What does mass number tell