CHEMISTRY 1 [SEM1Q1] - LESSON 3-4

Atom

Basic unit of matter that can retain its chemical properties and can enter into chemical reactions.

• Neutrons (n⁰)

• Protons (p⁺)

• Electrons (e^-)

Sub-Atomic Particles:

Plum Pudding Model

• Positively charged pudding with electrons are present

• Currently obsolete

Rutherford’s Model

• The middle atoms are heavy, thus positively charged particles were discovered.

• Although it did not describe the orbital movement of electrons.

Chadwick’s Model

• Proved the existence of neutrons

Bohr’s Model

• Introduced rings (orbits) which talked about the energy levels

• Electrons are traversing designated paths which surround the heavy nucleus

Schrödinger’s Model (Quantum Model)

• Has s,p,d,f orbitals which have several possible orientations in the 3d space

• Possible orientations tell you where the orbitals are

→ s: 1

→ p: 3

→ d: 5

→ f: 7

• Quantum numbers describe orbitals (location of the electron)

Quantum numbers

 describe orbitals (location of the electron)

• One-dimensional model where electrons orbited around the nucleus in a well-defined path known as “orbits”.

  • His old theory (Old Quantum Theory) is currently not accepted as it did not describe the electron’s wave-like characteristic.

  • This is now deemed obsolete except:

• The energy of an electron is “quantized” because it has pre-determined levels.

• Light is emitted as e^- moves from one energy level to a lower energy level

• De Broglie (1924) reasoned that e^- is both a particle and a wave.

  • duality nature of electrons

Read about:

Bohr’s Atomic Model

One-dimensional

orbits

Bohr’s Atomic Theory is a ___ model where electrons orbited around the nucleus in a well-defined path known as “___”.

Old Quantum Theory

Bohr’s Theory is also called ___ because it is currently not accepted as it did not describe the electron’s wave-like characteristic.

quantized

• Bohr’s Theory is now deemed obsolete except:

• The energy of an electron is “___” because it has pre-determined levels.

Light

is emitted as e^- moves from one energy level to a lower energy level

De Broglie (1924)

• reasoned that e^- is both a particle and a wave.

  • duality nature of electrons

• Schrödinger’s Model (1926): 

  • Electrons move in a three-dimensional space and have wave-like properties too.

  • The location of electrons are based on probability instead of certainty.

• Though there is an equation, it is uncertain because the equation is only applicable to the ground state of hydrogen atoms which have 1 electron.

• 3 Quantum numbers describe the “orbitals” in which electrons can be found:

• principal (n) - size

• angular (l) - shape

• magnetic (m_l) - orientation

• Banks on the concept of electron density, that gives the probability of finding an electron in a particular region of an atom. 

• His equation involves both particle behavior (mass) and wave behavior (wave function, psi) of submicroscopic particles, which depends on the location in space of the system.

Read about:

Schrodinger’s Quantum Model

Schrödinger’s Model (1926): 

• three-dimensional

• probability

• Electrons move in a ___ space and have wave-like properties too.

• The location of electrons are based on __ instead of certainty.

Though there is an equation, it is uncertain because the equation is only applicable to the ground state of hydrogen atoms which have 1 electron.

Why is it that even though we have the Schrodinger’s equation, the location of electrons remain uncertain?

• principal (n) - size

• angular (l) - shape

• magnetic (m_l) - orientation

3 Quantum numbers describe the “orbitals” in which electrons can be found:

• particle behavior (mass)

• wave behavior (wave function, psi)

Schrodinger’s equation involves both ___ and ___ of submicroscopic particles, which depends on the location in space of the system.

Electron Density

• The square of the wave function defines the distribution of electron density in a 3-D space around the nucleus.

  • High ED means a high probability of locating the electron.

Atomic Orbital

• It is the wave function of an electron in an atom that has a characteristic energy and distribution of electron density.

  • These are regions around the nucleus where electrons can probably be found (s, p, d, or f).

Heisenberg Uncertainty Principle

It states that If electrons are traveling at quantum speeds like a wave, then it is impossible to know its exact location and momentum simultaneously with certainty.

Quantum numbers

• Describes the orbitals (“address of electrons”)

  • Spin (m_s) - charge

  • Principal (n) - size and energy 

  • Angular (l) - shape

  • Magnetic (m_l) - orientation

• The answer must follow the PAMS format:

  • n, l, m_l, m_s

Principal (n)

• It is the size and energy of the orbital

  • Higher n - higher energy of an orbital, larger orbital, further it is from the nucleus

  • Lower n - low energy of an orbital, smaller orbital, close to nucleus

• ex. The 2 electrons in a Helium atom

Angular or Azimuthal (l)

• It is the shape of the orbital (integral no. from 0 to n-1)

  • l is based on the value of “n”.

  • The possible value of l of an electron may be drawn from the equation (n-1).

• Inferences:

  • s: l = 0

  • p: l = 1

  • d: l = 2

  • f: l = 3

• ex. The 2 electrons in a Helium atom

Magnetic (m_l)

• It is the orientation of the orbital in space

• It has integral values between -l and +l including 0. 

  • Number Line Technique - Creating a number line containing the negative and positive l values

• ex. 3d subshell

Spin (m_s)

• It is the spinning motion of an electron when placed in an external magnetic field.

  • Clockwise (up) - m_s = +½

  • Counter-clockwise (down) - m_s = -½

• Pauli’s Exclusion Principle:

  • No 2 electrons in an atom can have the same set of 4 quantum numbers.

  • The maximum of 2 electrons can occupy an orbital and they must have opposite spins (+½ or -½)

• ex. The 2 electrons in a Helium atom

Pauli’s Exclusion Principle

• No 2 electrons in an atom can have the same set of 4 quantum numbers.

• The maximum of 2 electrons can occupy an orbital and they must have opposite spins (+½ or -½)

• ex. The 2 electrons in a Helium atom

Electron Distribution

tells the arrangement of electrons in the energy levels, subshells, and orbitals around an atom’s nucleus.

Electron configuration

• Parts:

  • 1s¹ 

• 1 = energy level/size of orbital/n

• s = type of orbital (subshell)

• ¹ = no. Of electrons in this orbital (subshell)

Noble Gas Configuration

• For elements with high atomic number

• Use of Noble Gas core symbols

  • Written as an element symbol inside a bracket [ ], followed by the orbital with the highest principal number (n).  

  • Represented by the noble gas that belongs to the row before that of the element questioned.

Orbital Diagram

• Boxes and arrows represent the orbitals and the electrons

• The up and down orientation represent the magnetic spins of the electrons

• Aufbau Principle

• Pauli’s Exclusion Principle

• Hund’s Rule of Maximum Multiplicity

3 general rules and principles

Aufbau Principle

• Electrons should occupy first the orbitals with lower energy before those with higher energy.

Pauli’s Exclusion Principle

 No two electrons in an atom can possess the same set of quantum numbers.

Hund’s Rule of Maximum Multiplicity

The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins.

Z | atomic no.

 no. of protons in the nucleus of each atom of an element

A | mass no.

total no. of neutrons + protons present in the nucleus (decimals)

Isotopes

are atoms that have the same atomic no. but different mass numbers.

In isotopes, the protons have the same no. while the neutrons have diff no.

In isotopes, the ___ have the same no. while the ___ have diff no.

Read

Read

• protium

• deuterium

• tritium

3 isotopes of hydrogen

Read