introduction to the periodic table
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Introduction to the Periodic Table. alkali. Alkaline earth. Noble gas. halogens. . . I. History of the Periodic Table. Demitri Mendeleev (1860’s Russia) Arranged known elements: by mass - PowerPoint PPT PresentationTRANSCRIPT
Introduction to the Periodic Table
alkaliAlkaline earth
<---transition-------------------->
<-----------------Inner transition------------------>
halogens
Noble gas
I. History of the Periodic TableDemitri Mendeleev (1860’s
Russia)• Arranged known
elements:– by mass– in vertical columns by
Phs/Chem Prop.• Left blank spaces
(very accurate!)• Published his PT in 1871
Henry Mosley (1913)• Found a way to determine the atomic
number of elements using their emission frequency
• Arranged the PT by atomic number• “Father” of the modern periodic table
As time passed:*more elements were discovered*when placed by P/C properties, masses
were out of order
II. The Modern Periodic Table• Arises from Periodic
Law:A. Includes:
1. periods/rows2. groups/families
• There are 4 categories of groups:
1. Representative (also Main Group Elements)
2. Transition elements 3. Inner transition (also
Lanthanide and Actinide) 4. Noble Gases
• Some groups have special names: – 1A (Alkali Metals)– 2A (Alkaline Earth Metals)– 7A (Halogens)– 8A I (Noble Gases)
• The letters A and B in the group distinguish families – A = representative – B = transition
Properties and TrendsElectron Configurations
Metallic Character
i) L to R: metals to nonmetals
ii) Nonmetals are at the right of the Table. They tend to be insulators and react easily with metals.
iii) Metalloids separate the metals and nonmetals and have intermediate properties
iv) Noble Gases exist at the extreme right, are chemically stable and have full valence shells
Atomic Radius– Atomic radius – half distance between the nuclei of two
atoms of same element• Shielding effect – inner energy levels ‘shield’ the outermost
electrons from the positive charge pull of the nucleus– Atomic radius increases as you move down the groups• Great distance (adding energy levels) from nucleus = less pull
towards center– Decreases as you move left to right• More pull from nucleus (more protons), but no new distance
– EXCEPTION: Noble Gases – much bigger than group 17 – full outer shell
Atomic Radii
Ionization Energy– Ion – atom which has gained or lost electrons• Cation – (+) charged ion (lost e-)• Anion – (-) charged ion (gained e-)
– Ionization energy – the energy that is required to remove an e- from an atom
– Decreases as you move down the periodic table• Outermost electron gets further from nucleus, easier to pull off
– Increases as you move left to right• No more distance from nucleus, but higher charge = held more
tightly
Ionization Energy
Electron Affinity– Electron Affinity – the energy change that occurs when
an electron is ADDED to a neutral atom• Bigger negative number = easier to add e-
– Harder to add as you go down a group• Further distance from nucleus & more inner e- = more
repulsion felt from e-
– Easier to add from left to right• Increased nuclear charge = more attraction to nucleus (+)• Noble Gases – don’t accept e-
– Halogens gain most easily, they want to complete that ‘perfect eight’
Electron Affinity
Electron Affinity & Ionization Energy
Ionization Energy vs. Electron Affinity
Ionic Size (Radius)
– Ionic Radius- ½ the distance between the nuclei of two ions
– Cations (+) are always SMALLER than neutral atom• Nuclear charge the same, less e- = strong pull inwards
– Anions (-) are always LARGER than neutral atom• Nuclear charge the same, MORE e- = less pull inwards
– Increases as you go down a group– Decreases from left to right
Electronegativity
–Electronegativity – tendency for an element to have a stronger pull on the shared e- in a covalent bond (values btwn 0-4)–Decreases down a group – less likely to
keep the shared e-
–Increases from left to right – more likely to have the shared e-
Electronegativity