ch. 1 atomic structure september 11, 2016 chapter #1 ... chem... · ch. 1 atomic structure...

Ch. 1 Atomic structure September 11, 2016

Democritus (460-340 BC)Democritus believed that all matter consisted of extremely small particles that could not be divided. He called them atoms from the Greek word atomos meaning "uncut".

Atomic Theories

Chapter #1 - Atomic Structure

John Dalton (1766-1844) Dalton's model was that the atoms were tiny, indivisible, indestructible particles, and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were.

Dalton's Atom Model


J.J Thomson (1856 - 1940) - atom is a ball of positive charge containing a number of electrons.

Plum Pudding model

Experiment: Cathode Ray Tube

Cathode Ray Tubes were in nearly every home in the old TV and computer monitors.

Atoms – an atom is the smallest unit of matter. Each kind of atom is called an element.

Ernest Rutherford (1871 – 1937) Gold Foil Experiment.Discovery of the nucleus 1908


Atoms are mostly empty space most of an atom’s mass is concentrated in a small positively charged region called the nucleus.

Niels Bohr - proposed the Planetary Model for the hydrogen atom in 1913. Electrons move in definite orbits around the nucleus, like planets. He proposed that each electron moves in a specific energy level.


Electron Shells - Energy LevelsDraw the Bohr energy levels diagrams for H, Li, and Na.


An electron in an atom can move from one energy level to another when the atom gains or loses energy.

Light

Energy

Atomic Line Spectrum


Atomic Line Spectrum

Each type of atom (H2, O2 He, ) gives off a unique set of colors. The colored lines (or Spectral Lines) are a kind of "signature" " fingerprints" for the atoms.

• Schrodinger's view of the atom can be seen as "layers within layers" in terms of the electron shells.

• Each electron shell is made up of a number of subshells. The number of subshells in a shell is the same as the shell number.

• These subshells can be further subdivided into orbitals, and each orbital is a distinct region of space that can contain a maximum of two electrons.

Schrodibger's cat BB

Electron Cloud – the space around the nucleus of an atom which describes the possible location of where the electrons can be found.

Schrodinger developed the Wave Model which suggests that electrons behave in a wave-like manner


The Cloud Model, Electrons do NOT move about the atom in a definite path and it is impossible to determine the exact location of an electron. Scientists can only predict the probable location of an electron.

Bohr's idea of energy levels, however, is still used.

The exact location of the electrons within an orbit could not be precisely calculated.

The uncertainty principle states that the position and velocity cannot both be measured,exactly, at the same time

Heisenberg "Uncertainty Principle"

SummaryModels of the Atom


Energy Levels and Orbitals (shells) Building Model

Energy

Atomic Orbitals are mathematical descriptions of where the electrons are in an atom (or molecule) are most likely to be found.

Each orbital has a name. The orbital occupied by the hydrogen electron is called a 1s orbital. • The "1" represents the fact that the orbital is in the first energy level. • The "s" tells you about the shape of the orbital. "s" orbitals are spherically symmetric around the nucleus

Every energy level has an "S" orbital

Each orbital can only hold 2 electrons.


p orbitals begin at the second energy level

At the first energy level, the only orbital available to electrons is the 1s orbital, but at the second level, as well as a 2s orbital, there are also orbitals called 2p orbitals.

At any one energy level there are three absolutely equivalent p orbitals. These are given the symbols px, py and pz.

At the third level, there is a set of five d orbitals as well as the 3s and 3p orbitals (3px, 3py, 3pz). At the third level there are a total of nine orbitals altogether.

At the fourth level, as well the 4s and 4p and 4d orbitals there are an additional seven f orbitals - 16 orbitals in all.

s, p, d and f orbitals are then available at all higher energy levels as well.

Atomic Orbitals


Shorthand Electron ConfigurationTo simplify the writing of lengthy electron configurations, the symbol of a noble gas may be substituted for the appropriately filled shells and orbitals.

The arrangement of electrons in the orbitals of an atom.

Electron Configurations


Pauli Exclusion Principle

The blue electrons are pairedThe red electrons are unpaired

Hund’s Rule – electrons will not pair in an orbital until all orbital of equal energy contain one electrons.

An orbital can hold a maximum of 2 electrons. They must spin in opposite directions, they are said to be paired.


• Protons - are positively charged particles, have a mass of 1 amu, found in the nucleus. They determine which element an atom is.

• Neutrons - are neutral particles, have a mass of 1 amu, found in the nucleus. • Electrons - are negatively charged particles, have a mass of 1/1840

amu. They orbit the nucleus

Subatomic Particles


Atomic Number is the number of protons in the nucleus of an atom.(also represent the number of electrons in the neutral atom)Mass Number = the number of protons + neutrons in the element’s nucleus.Used to identify isotopes.

Practice:

Ion – An atom with an overall positive or negative charge. Cation - When a neutral

atom loses an electron(s), it has more positive protons than negative electrons. This results in an overall positive charge.

Anion - When a neutral atom gains an electron(s), it has less positive protons than negative electrons. This results in an overall negative charge.


Isotopes – are atoms of the same element whose nuclei contain the same number of protons but different number of neutrons.

Isotopes of hydrogen

One element may have several different isotopes.

Various Isotopes:

Stable

Stable

Unstable

ch. 1 atomic structure september 11, 2016 chapter #1 ... chem... · ch. 1 atomic structure...

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