Atom and Periodic Table of elements

◦ History of Atom Democritus(460 B.C)-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

Ernest Rutherford(1911)-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.

Erwin Schrödinger -Electron is like a wave

James Chadwick (1932 )-discovered neutron.-The proton-neutron together, received the name, "nucleon." Werner Heisenberg-intruduced Quantum mechanical model.-model introduced the concept of sub-energy levels.

Characterising an atom-Mosley discovered atoms of elements are different from each other.-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.

Characterising electrons.-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.-atomic orbitals(s,p,d,f)

Electron configuration - 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 after another.

- 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

Element# of Electrons in El-

ementElectron Configura-

tion

He 2 1s2

Li 3 1s22s1

Be 4 1s22s2

O 8 1s22s22p4

Cl 17 1s22s22p63s23p5

K 19 1s22s22p63s23p64s1

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 columnHistory 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 chemistsJohann Dobereiner- the atomic weight of elements possessing similar chemical properties.-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.John Newlands-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 the table.Dmitri Ivanovich Mendeleev-reordered elements despite their accepted masses.- published the table of elementsHenry Mosley-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 properties.

groups of the periodic table1.Alkali metals(IA)2.Alkaline earth metasls(IIA)3.Halogens(VII)4.Noble gasses(VIIIA)5.transition metals

Atomic trends(properties)Atomic Radius -The size of the electron cloud increases as the principal quantum number increases the positive charge on the nucleus increases by one proton Ionization Energy -The ionization energy tends to increase as atomic number increases in any horizontal row or period. Electron Affinity

-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.

Chemical BondingChemical bond-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 form moleculesBond– valence electrons rearranged to make atom more stableWay they are rearranged depends on type of bond.Types of chemical bondingIonic bonding- chemical bonding that results from the electrical attraction between large numbers of cations and anions.-metal-nonmetal

In forming compounds, atoms tend to gain or lose elec-trons 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 octet 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.

Covalent bonding- results from the sharing of electron pairs between two atomsIn purely covalent bond, electrons shared equally between two atoms. METALLIC BONDING- 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 in space

Notes

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Prepared by:Jonalyn(J.C) Timbal