General Chemistry
Asst. Prof. Dr. Waralee W.
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Chemistry
“The study of the composition of matter,
and the changes that it undergoes.”
Why should we study chemistry?
Chemistry is the central science and impacts on all facets of
our lives.
An understanding of chemistry is necessary to all other
sciences from astronomy to zoology.
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We are made of elements.
By mass, about 96 percent of the human
body is made from four elements:
oxygen, carbon, hydrogen and nitrogen.
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https://www.quora.com/What-chemical-elements-make-up-the-human-body
Some of the elements are also present in the human body, and
without them, life would be impossible.
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https://www.livescience.com/51417-how-elements-in-fireworks-make-the-human-body-work-infographic.html
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Language of Chemistry
The “ELEMENTS”, their names,
and symbols are given on the
PERIODIC TABLE
How many elements are there?
118 elements have been identified (dated 28 November 2016):
• 82 elements occur naturally on earth.
• 36 elements have been created by scientists.
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https://iupac.org/what-we-do/periodic-table-of-elements/
Chemistry of Atoms



ATOMS
the smallest indivisible particle of an element
exist alone or enter into chemical combination
MOLECULES
a combination of atoms that has its own
characteristic set of properties
Models of the Atom Timeline
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https://www.youtube.com/watch?v=NSAgLvKOPLQ
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Atomic Theory
Dalton’s Atomic Theory
(1804)
 All matter is composed of extremely small particles called atoms.
 Atoms of a given element are identical in size, mass, and other
properties. Atoms of different elements differ in size, mass, and other
properties.
 Atoms cannot be subdivided, created, or destroyed.
 Atoms of different elements can combine in simple whole number
ratios to form chemical compounds.
 In chemical reactions, atoms are combined, separated, or
rearranged.
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https://www.ck12.org/chemistry/daltons-atomic-theory/lesson/Dalton%E2%80%99s-Atomic-Theory-CHEM/
Dalton’s atomic theory has been largely accepted by
the scientific community, with the exception of three
changes:
(1) an atom can be further sub-divided
(2) all atoms of an element are not identical in mass
(3) using nuclear fission and fusion techniques, we can
create or destroy atoms by changing them into other
atoms.
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https://www.ck12.org/chemistry/daltons-atomic-theory/lesson/Dalton%E2%80%99s-Atomic-Theory-CHEM/
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Rutherford’s Model of Atom
(1911)
https://www.britannica.com/science/Rutherford-atomic-model
 Atom is composed mainly of vacant space.
 All the positive charge and most of the mass is in
a small area called the nucleus.
 Electrons are in the electron cloud surrounding
the nucleus.
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LIMITATIONS OF RUTHERFORD’S ATOMIC MODEL
 Behavior of the electron was much more complicated than the one
shown in the Rutherford model.
 The electrons did not move in the set specific paths and also their
location around the nucleus was able to change on the basis of the
energy that they possessed. Thus, no longer could it assume that
the electrons moved in straight paths.
 Currently, the electron cloud model is the current model of the
atom.
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http://www.justscience.in/articles/what-was-the-rutherfords-atomic-model/2017/06/29
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Niels Bohr’s Model of Atom
(1913)
http://thehistoryoftheatom.weebly.com/niels-bohr.html
Niels Bohr was coupling Rutherford postulation with Max Planck
quantum theory, proposed that atom consists of a positively
charged nucleus of protons and neutrons surrounded by
negatively charged electrons traveling in discrete orbits at a
fixed distance from the nucleus.
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 Bohr model was based on his observations of the atomic
emissions spectrum of the hydrogen atom.
 When white light is diffracted with a prism, all the colors of
the visible spectrum can be seen.
 Each color corresponds to a specific amount of energy;
however when the light given off by the hydrogen atom was
passed through a prism, only certain colors of light could be
seen.
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https://chemistry.tutorvista.com/inorganic-chemistry/spectral-lines.html
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The experiment explains –
1.Electrons would have only certain chemical motions.
2.Electrons in atoms orbit nucleus in orbits that have a set size and energy.
3.When electrons move or jump from one orbit to another one, electrons
absorbed or emitted the radiation with a frequency determined by the
energy difference of the energy levels according to Planck relations.
 wavelength of absorbed or
emitted lights is exactly such that
the photon carries the energy
difference between two orbits.
 The energy can be calculated by
using following equation.
E = hc/λ
Where,
h = Plank constant
c = Speed of light
λ = Wavelength of light
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https://chemistry.tutorvista.com/inorganic-chemistry/niel-bohr-atomic-theory.html
Bohr Model explained line spectrum
 Electrons in atoms are in orbits of differing energy around the
nucleus (think of planets orbiting around the sun).
 Energy levels (or shells) describe these orbits of differing energy.
The energy of an electron is quantized; electrons can have one
energy level or another but nothing in between.
 The energy level an electron normally occupies is called ground
state. But it can move to a higher-energy, less-stable level, by
absorbing energy. This higher-energy, less-stable state is called
the excited state.
 After it’s done being excited, the electron can return to its original
ground state by releasing the energy it has absorbed.
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Bohr's contribution to science
 Niels Bohr postulated atomic theory
based on quantum theory that the
negatively charged electrons travel
around the positively charged nucleus
in a stationary orbit.
 This also led to the theory of the
different energy levels in atoms, that is
if an electron transmits from higher
orbit level to a lower level orbit it must
release energy or electromagnetic
radiation.
 Niels Bohr contributed the quantum
theory of atomic structure and today’s
research of quantum physics which is
our future.
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Structure of Atom
Atoms were created after the Big Bang 13.7 billion years ago. As the
hot, dense new universe cooled, conditions became suitable for quarks
and electrons to form. Quarks came together to form protons and
neutrons, and these particles combined into nuclei. This took place
within the first few minutes of the universe's existence.
Composed of:
 Protons
 Neutrons
 Electrons
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https://www.livescience.com/37206-atom-definition.html
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Protons
 found in nucleus
 relative charge of +1
 relative mass of 1.0073 amu
Neutrons
 found in nucleus
 neutral charge
 relative mass of 1.0087 amu
Electrons
 found in electron cloud
 relative charge of -1
 relative mass of 0.00054 amu
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Atomic Symbol
 Each element is assigned a unique symbol.
 Atomic symbol is 1-2 letters and the first is capitalized.
 Symbol may not match the name, often had a different
name to start with.
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Atomic numbers, mass numbers, and
Isotopes
A unique chemical symbol, X
 Every atom of an element has
the same number of electrons
and protons.
 The atomic number Z number of protons in the
nucleus of an atom.
 The mass number A - the
number of protons plus the
number of neutrons in the
nucleus.
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https://en.wikipedia.org/wiki/Symbol_(chemistry)#/media/File:Atomic_Symbol.jpg
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Complete symbol for neutral atom of berylium
with ____ protons, ____ neutrons, and ____ electrons
Complete symbol for neutral atom of chlorine
with ____ protons, ____ neutrons, and ____ electrons
Complete symbol for neutral atom of sulfur
with ____ protons, ____ neutrons, and ____ electrons
Complete symbol for sodium ion
with ____ protons, ____ neutrons, and ____ electrons
Complete symbol for berylium ion
with ____ protons, ____ neutrons, and ____ electrons
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 Although each atom of an element has the same number of
protons, the number of neutrons can vary. Atoms of an element
with different number of neutrons are called isotopes.
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https://study.com/cimages/multimages/16/isotopesofhydrogen.png
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 the atomic masses of elements in the
periodic table are rarely ever whole
numbers, like the atomic mass of
carbon is 12.011.
 The atomic mass of carbon is based
on the average atomic masses of its
isotopes and the abundance of each
isotope.
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https://study.com/cimages/multimages/16/carbonatomicmass.png
Problems
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Do You Understand Isotopes?
How many protons, neutrons, and electrons are in
14 C ?
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6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are in
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C?
___ protons, ___ (11 - 6) neutrons, ___ electrons
2.3
A molecule is an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5
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An ion is an atom, or group of atoms, that has a net
positive or negative charge.
Cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
2.5
A monatomic ion contains only one
atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
2.5
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Do You Understand Ions?
How many protons and electrons are in
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3+
13 Al ?
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in
78 Se 2- ?
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__ protons, __ (34 + 2) electrons
2.5
2.5
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Atomic Orbitals
 Atomic orbitals are regions of space around the nucleus of an
atom where an electron is likely to be found.
 Specifically, atomic orbitals are the quantum states of the
individual electrons in the electron cloud around a single atom.
 The most commonly filled orbitals are s, p, d, and f. These orbitals
have different shapes (e.g. electron density distributions in space)
and energies (e.g. 1s is lower energy than 2s; 2s is lower energy
than 2p)
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 S orbitals have no angular nodes and are spherical. P orbitals
have a single angular node across the nucleus and are shaped
like dumbbells. D and f have two and three angular nodes,
respectively.
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https://chemistry.stackexchange.com/questions/31189/what-is-spdf-configuration/
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Rules for Assigning Electron Orbitals
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http://spmchemistry.onlinetuition.com.my/2012/12/electron-arrangement-in-atom.html
https://www.quora.com/What-are-some-examples-of-electron-arrangements
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Electron configuration
 Representation of the arrangement of electrons distributed among
the orbital shells and subshells.
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https://files.mtstatic.com/site_4334/1218/
Electron Configuration
 The electrons in an atom fill up its atomic orbitals according to the
Aufbau Principle; "Aufbau" in German, means "building up."
The Aufbau Principle states electrons always fill orbitals of lower
energy first. 1s is filled before 2s, and 2s before 2p.
 Pauli Exclusion Principle states no two electrons within an atom
can have identical quantum numbers. This principle means that if
two electrons occupy the same orbital, they must have opposite
spin.
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Electron Configuration
 Hund's Rule states that when an electron joins an atom and has
to choose between two or more orbitals of the same energy, the
electron will prefer to enter an empty orbital rather than one
already occupied.
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http://www.sparknotes.com/chemistry/fundamentals/atomicstructure/section2/
Practice
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D-BLOCK ELEMENTS
Some elements do not follow this filling order exactly.
When a transition metal loses electrons to form a cation, the first two
electrons to be removed are the s ones, then the d. Why?
 Completely filled sublevels are more stable than partially filled
sublevels.
 A sublevel which is exactly half filled is more stable than a partially filled
sublevel which is not half full.
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ucdavis.edu
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https://villanovachemistry.wordpress.com/electron-configuration-anomalies/
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Problem. Electron configuration
Fill in the blank
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https://online.science.psu.edu/chem101_activeup/node/4465
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