Atom and Periodic Table of elements
◦ History of Atom
-develop the idea of atoms.
- atomos (basic matter particles)
John Dalton (1800's )
-elements are made up of atoms
-atoms could not be destroyed, created, or divided
since they are the smallest particles.
J.J. Thomson (1897 )
-discovered the electron and proposed a model for the structure
of the atom.
-electrons had a negative charge and thought that matter must
have a positive charge.
-atoms are electrically neutral
-atoms consist of a compact positively charged nucleus,
-electorns are around the nucleus.
Niels Bohr (1912 )
-derived rutherford's idea by adding electrons in specific orbit.
-Electron is like a wave
James Chadwick (1932 )
-The proton-neutron together, received the name, "nucleon."
-intruduced Quantum mechanical model.
-model introduced the concept of sub-energy levels.
Characterising an atom
-Mosley discovered atoms of elements are different from each
-proton/atomic number distinguishes an element.
-sum of neutron and proton are the mass number.
-Atoms are neutral.
-the difference between mass and protons are neutron.
-atomic orbitals is the volume around the nucleus.
-electron energy relates to the size of the atomic orbital.
-the farther distance of electron the bigger the size of the atomic
orbital and the greater of its energy.
-main energy level (n) are called where orbital are found.
- The electron configuration of an atom is the particular
distribution of electrons among available shells.
- it has valence shell and valence electron.
- It is described by a notation that lists the subshell symbols, one
- The notation for electron configuration gives the number of
electrons in each subshell.
- The number of electrons in an atom of an element is given by
the atomic number of that element.
sublevel orbital maximum # of electrons
s 1 2
p 3 6
d 5 10
f 7 14
# of Electrons in
He 2 1s2
Li 3 1s2
Be 4 1s2
O 8 1s2
Cl 17 1s2
K 19 1s2
Periodic Table of Element
periodic table of element
--is a tabular display of the chemical elements, organized on the
basis of their properties. Elements are presented in
increasing atomic number.
-element identified by its symbol.
-made out of rows of elements and column
History of development
- By 1869, a total of 63 elements had been discovered.
-a vast body of knowledge concerning the properties of elements
and their compounds was acquired by chemists
- the atomic weight of elements possessing similar chemical
-proposed that nature contained triads of elements
ordered by the atomic weight (the Law of Triads).
-Triads is a set of three elements with same properties.
-classified the 56 established elements into 11 groups based on
similar physical properties.
-proposed the Law of Octaves stated that any given element will
exhibit analogous behavior to the eighth element following it in
Dmitri Ivanovich Mendeleev
-reordered elements despite their accepted masses.
- published the table of elements
-rearranged the elements in order of their atomic number.
The Periodic Law
-elements are arranged in order of increasing atomic number.
-can be group into three
classes(metals,nonmetals,metalloids)based on their general
groups of the periodic table
2.Alkaline earth metasls(IIA)
-The size of the electron cloud increases as the principal
quantum number increases
the positive charge on the nucleus increases by one proton
-The ionization energy tends to increase as atomic number
increases in any horizontal row or period.
-The attraction of an atom for an electron.
-The general trend as you go down a column is a decreasing
tendancy to gain electrons.
- As you go across a row there is also a trend for a greater
attraction for electrons.
-is a mutual electrical attraction between the nuclei and valence
electrons of different atoms that binds the atoms together
Valence Electrons -A Valence electron is an electron in the
outer shell of an atom which can combine with other atoms to
– valence electrons rearranged to make atom more stableWay
they are rearranged depends on type of bond.
Types of chemical bonding
- chemical bonding that results from the electrical attraction
between large numbers of cations and anions.
In forming compounds, atoms tend to gain or lose
electrons in order to achieve the electron configuration
of a noble gas
Key Concept Atoms of metals lose their valence electrons.
Atoms of some nonmetals ten to gain electrons or to share
with other nonmetallic elements to achieve a complete
Formation of Cations -When an atom loses an electron it
produces a positively charged ion, or a cation. The most
common cations are those produced by the loss of valence
electrons from metal atoms. Electron–Dot Structures for
Ions Remove electrons for cations
Formation of Anion -The gain of negatively charged
electrons by a neutral atom produces an anion.
- results from the sharing of electron pairs between two atomsIn
purely covalent bond, electrons shared equally between two
- metallic bonding usually occurs in metals, such as copper.
- The valence electrons of these atoms are free to move about
the piece of metal and are attracted to the positive cores of
copper, thus holding the atoms together.
Lewis dot Structure
-the structure of carbon and its compound can be expressed
using the Lewis-dot structure This system identifies how the
atoms that compose a molecule of a specific compound are
attached (bonded) to one another and (to some extent) oriented
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