Early Models of the Atom
What do we still believe is correct about Dalton’s Atomic Theory?
How many total atoms are in three NaOH molecules?
How many
electrons would fit inside a hydrogen atom?
Summarize Thomson’s
experiment and his data.
Match the
following scientists and their
accomplishments. a. Dalton b. Thomson c. Millikan d. Chadwick __ oil drop
experiment and the properties of the electron
__ discovered the proton and its location __ used the cathode ray tube to discover the electron
__ said particles are indivisible
Chapters 5 and 13: Atomic Structure
Dalton’s Atomic Theory
1. All elements are composed of tiny ____________particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element
are ______________ from those of any other element.
3. Atoms of different elements can physically combine with one another in simple whole-number to form compounds.
4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.
Atom – the smallest particle of an element that retains the properties of that element. Example: How many atoms are in each compound?
CO2 : H2O : H2SO4 :
Electron
- negatively charged subatomic particle. They have a –1 charge and are 1/1840 the mass of a ______________ atom
Cathode Ray Tube (CRT)
- device used to originate a flow of charged particles
J.J. Thomson - credited with _____________________________
• He used CRT's to measure deflection of charged rays using different gasses, magnets, and different metal electrodes.
• Found that the ray moved from the cathode (-) to the anode (+)
• He proposed that the ray was composed of negatively charged particles which he called electrons.
• He also calculated the ____________________________ of the electron.
Robert Millikan –
His studies led to the determination of the properties of the electron in 1916.
Proton – positively charged subatomic particle discovered by Goldstein. Neutron - discovered by James Chadwick 1932.
• Has approximately the ____________________ as a proton. • They are located in the nucleus.
• It has no charge.
What is the Plum Pudding Model?
How was the nucleus discovered?
In the space below, draw an atom of carbon with 6 protons, neutrons and electrons.
If protons + neutrons = mass number, then how many neutrons are present in an atom of potassium-22?
Draw the isotopes of beryllium. Be-8
Be-9
Be-11
Thomson proposed the “Plumb Pudding” Model of the atom.
Rutherford – credited with discovering the ____________________. • Gold Foil Experiment
Nucleus – the central core of an atom and is composed of protons and neutrons. • It accounts for more than _______ of an atom’s mass.
• The nucleus is also positively charged.
Atomic Number
– the number of _________________ in the nucleus of an atom. Example:
What is the atomic number for the following elements? Al C Br I Na Ag How many protons are there in each of the above?
Mass Number
– the number of protons and neutrons in the nucleus of an atom. Isotopes
– atoms that have the same number of protons but different numbers of neutrons. Example:
What is the number of neutrons in each of the following isotopes?
27Al 12C 80Br 127I 23Na 108Ag
Find the missing values for the NEUTRAL atoms in the table below.
Element Atomic # Mass # # protons # electrons # neutrons
12 25
6 6
K 40
23 28
___________________ – a weighted ______________ of the atoms in a naturally occurring sample of the element.
______________________ (amu) – is defined as one-twelfth the mass of a carbon-12 atom. Example:
A sample of cesium is 75% 133Cs, 20% 132Cs, and 5% 134Cs.
Draw a chemical symbol and circle the atomic mass.
How do you calculate atomic mass?
What energy level are the following elements in? Sr
Pb
The maximum number of orbitals in a particular energy level is equal to n2.
• The maximum number of electrons in a particular energy level is equal to 2n2.
13.2 Electron Configurations
• Electron configuration – ways in which electrons are arranged around the nuclei of atoms
Three rules for finding electron configurations:
• Aufbau Principle – electrons enter orbitals of lowest energy first.
• Pauli exclusion principle – an atomic orbital can contain at most two electrons. They must have opposite spins.
• Hund’s Rule – When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with parallel spins. Second electrons are added and are paired so that each orbital contains two electrons with opposite spins.
• Complete the orbital diagrams below: 1s 2s 2p 3s
• H __ __ __ __ __ • He __ __ __ __ __ • O __ __ __ __ __ • Na __ __ __ __ __ __
Compare this value to that of the periodic table. Is it accurate?
Calculated Value: Periodic Table:
________ amu 132.905 amu
13.1 Evolution of Atomic Models
The work of Dalton, Thomson and Rutherford began an age of exploration that culminated with a model of the atom that described a dense nucleus surrounded by electrons. This model continued to be modified as more data was collected.
• Bohr
– Electrons are arranged in concentric circular paths (orbits) around the nucleus – Called the ___________________ model
– Electrons have particular paths with fixed energy, which he called its energy level • Quantum Mechanical Model – Modern description of the electrons in atoms
– It comes from the mathematical solutions to the Schodinger equation.
– The probability of finding an electron within a certain volume of space surrounding the nucleus can be represented by a cloud (electron cloud).
– The cloud represents where the electron can be found approximately 90% of the time.
In the top box, draw a picture of the model developed by each scientist. In the bottom box, describe the model. Dalton’s model is done for you.
Dalton Thomson Rutherford Bohr Quantum
Mechanical Model
The atom is a solid, indivisible sphere
• Energy level
– region around the nucleus where the electron is likely to be moving – electrons can “jump” from one energy level to another
• Quantum
– the amount of energy required to move an electron from its present energy level to the next higher ______________________________
• Atomic orbital
– the region in space where the electron is likely to be found • Locations of Electrons in an Atom
– Electrons can be described by a series of four quantum numbers • Principal quantum number (n)
What would the quantum numbers be for the outer electron of a chlorine atom?
Write the electron configurations for the following: He:____________ _______________ Na:____________ _______________ Ti:_____________ _______________
– Azimuthal quantum number (l)
• Describes the shape of the atomic orbital
• s orbitals are spherical, p orbitals are peanut shaped, d orbitals are daisies and f orbitals are fancy
• Designates a sublevel
• Values from 0 up to and including (_______) • l = 0, 1, 2, 3…,(n-1)
– There are two other quantum numbers that describe the position and spin, but you will not need to know them.
13.2 Electron Configurations
• Electron configuration – ways in which electrons are arranged around the nuclei of atoms
Three rules for finding electron configurations:
• Aufbau Principle – states that electrons enter orbitals of _____________ energy first. • Pauli exclusion principle – states that an atomic orbital can contain no more than two
electrons. They must have ____________________________.
• Hund’s Rule – When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with parallel spins. Second electrons are added and are paired so that each orbital contains two electrons with opposite spins.
• Complete the orbital diagrams below: 1s 2s 2p 3s
• H __ __ __ __ __ • He __ __ __ __ __ • O __ __ __ __ __
• Na __ __ __ __ __ __
Complete the following by circling an answer: As the wavelength of wave increases/decreases, the frequency will increase/decrease.
13.2 Light and Atomic Spectra
• Electromagnetic Radiation – a series of ____________________ that includes radio waves, microwaves, visible light, infrared and ultraviolet light, x-rays, gamma rays.
Diagram of a wave:
• Amplitude – wave’s height from origin the crest.
• Wavelength(l) – the distance between ________________.
• Frequency (ƒ) – the number of wave cycles to pass a given point per unit time. (Hz or s-1)
• v = c/l
Try to rearrange the light formula in at least two ways.
EXAMPLE: A wave of yellow light has a frequency of 2.73 x 1016s-1. Calculate its wavelength.
ƒ = c = 3.00 x 108 m/s l = ?
• Spectrum – series of colors produced when white light is separated by a diffraction gradient (prism).
• ROY G. BIV
• Red light has the longest wavelength and the shortest frequency. ___________ ENERGY. • Violet light has the shortest wavelength and the highest frequency. HIGHEST ENERGY. Atomic emission spectrum – series of lines produced by passing the light emitted by an excited atom through a diffraction gradient. These spectra can be used in element identification.
Quantum Concept & the Photoelectric Effect
• Einstein proposed that light could be viewed as a stream of particles called photons.
• Max Planck believed that energy was emitted or absorbed by small units called quanta. He
found that the amount of energy released or absorbed was proportional to the frequency of the radiation.
• E = h ƒ
• E = Energy • ƒ = frequency
• h = Planck’s constant: 6.63 x 10-34 J∙s
EXAMPLE: Calculate the energy of an individual photon of yellow light having a frequency of 2.73 x 1016s-1.
