Download Atoms Ions Valence Electrons Isotopes

Atoms, Ions, Valence
Electrons, & Isotopes
Chemistry MYP
Ms. Khan
Atom Identity
Atom Identity
▪ atoms are identified by the number of protons within the nucleus
▪ known as the atomic number (Z)
▪ elements on periodic table in order by atomic number
▪ every atom has a mass number (A), measured in amu
– the mass number is the sum of the total number of protons and
neutrons in the nucleus
– each proton and each neutron contributes 1 amu
▪ atoms are electrically neutral unless otherwise indicated
Ions
Ions
▪ a charged atom
– exist when an atom has an unequal number of protons and
electrons
▪ charge on atom results from the loss or gain of electrons
– cation: positively charged atom (lost electrons)
– anion: negatively charged atom (gained electrons)
▪ each proton carries a +1e charge; each electron carries a
-1e charge
Valence Electrons
Valence Electrons
▪ the electrons available to be lost, gained, or shared in the
formation of chemical compounds
▪ typically, these are the electrons that exist in the highest
occupied energy level, maximum of 8
▪ the number of valence electrons can be determined from the
electron configuration
▪ example: an atom with 12 electrons, 1s2 2s2 2p6 3s2 , has
two valence electrons that exist at the third energy level
Inner-Shell Electrons
▪ the electrons that are not in the highest occupied energy level
▪ ex: an atom with 12 electrons, 1s2 2s2 2p6 3s2 , has 2
valence electrons that exist at the 3rd energy level and 10
inner-shell electrons that exist at the 1st and 2nd energy
levels
▪ ex: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d105p3
– 46 inner-shell electrons
– 5 valence electrons
Lewis Dot Diagram
▪ an
electron
configuration
notation in which only the
valence electrons of an atom of
a particular element are shown,
indicated by dots placed
around the element’s symbol
▪ also called electron-dot notation
▪ an electron is placed on each of
the four “sides” of the element
symbol before a second electron
is added to any side
Formation of Ions
▪ atoms form ions to satisfy the octet rule
– chemical compounds tend to form so that each atom, by
gaining, losing, or sharing electrons, has an octet of
electrons in its highest occupied energy level
▪ the number of valence electrons will either decrease to “0” or
increase to 8, whichever requires less energy
– an atom with 2 valence electrons will lose 2 electrons to
reach 0
– an atom with 6 valence electrons will gain 2 electrons to
reach 8
Isotopes
Isotopes
▪ atoms of the same element that have different masses,
therefore different mass numbers
– isotopes can be written as the element name followed by the
mass number
– ex: carbon with a mass number of 12
carbon-12
– ex: nitrogen with a mass number of 14
nitrogen-14
▪ mass of atom changes if the number of neutrons varies
between different atoms
▪ some isotopes of an element are more stable than others and
therefore more commonly found in nature
Dalton’s Atomic Theory
1. all matter is composed of extremely small particles called atoms
2. atoms of a given element are identical in size, mass, and other
properties; atoms of different elements differ in size, mass, and
other properties
3. atoms cannot be subdivided, created, or destroyed
4. atoms of different elements combine in simple whole-number
ratios to form chemical compounds
5. in chemical reactions, atoms are combined, separated, or
rearranged
Which postulate can now be disproven?
Nuclear Symbols
Nuclear Symbols
𝐴
0
𝑋𝑥
𝑍
▪ Xx = element symbol
▪ Z
= atomic number
▪ A
= mass number
▪ 0
= charge of atom
Periodic Symbol
47
Ag
107.868
silver
▪ atomic number (Z)
▪ element symbol
▪ average atomic mass
– NOT mass number (A)
▪ element name