Cha 6: Periodic Table & Periodic Law

Development of the Modern Periodic Table

Antoine Lavoisier: Known for conservation of mass; sorted elements.
John Newlands: Proposed the 'law of octaves'.
Dmitri Mendeleev: Created the first periodic table based on atomic mass.
Henry Moseley: Reorganized the periodic table by atomic number. We use his model today & give him full credit (:
- periodic law: the chemical and physical properties of elements repeat in a predictable pattern when arranged by their atomic number.

Mendeleev's model successfully predicted the existence of three elements discovered posthumously. (a good model predicts future discoveries)

Element Symbol: One or two-letter abbreviation for an element.
Atomic Number: # protons
Atomic Mass: Weighted average of all naturally occurring isotopes of an element.
Group: Vertical column with elements sharing similar chemical properties due to the same number of valence electrons.
Period: Horizontal row with elements having valence electrons in the same energy level.
Representative Elements: Found in groups 1, 2, 13-18, with transition elements in groups 3-12.

Shortcut for Electron Configurations: Use the symbol of a noble gas in square brackets followed by the electron configuration.
- For large atoms, writing out the whole electron configuration would be tedious. So, we use a condensed electron configuration. To write it, you use the noble gas. First, you place the preceding noble gas in brackets. Next, you write the remaining electron configuration.
  For example, Radium has the condensed electron configuration Rd: [Rn] 7s2.
  1. Radon is the preceding noble gas. We write Rd: [Rn].
  2. Radium completely fills the 7s orbital. So we write, Rd: [Rn] 7s2.
Valence Electrons and Group Numbers: Lab insights showed a connection between valence electrons and group numbers.
Electron Dot Structures: Representative elements in groups 13-18 (3-8) have varying valence electrons affecting reactivity.

Group 1 elements lose one electron (e.g., Na, K), while Group 7 elements gain one electron (e.g., F, Cl) during reactions.

Metals: Shiny, solid at room temperature, good conductors of heat and electricity; most representative and transition elements are metals.
Non-metals: Generally gases or brittle, dull-looking solids; poor conductors of heat and electricity.
Metalloids: Elements with properties of both metals and non-metals; e.g., Silicon (Si) and Germanium (Ge).
Transition Elements: Metals in the middle of the periodic table transitioning in properties from more metallic to less metallic.
Special Groups: Include Alkali Metals (Group 1), Alkaline Earth Metals (Group 2), Halogens (Group 7), and Noble Gases (Group 8).

Atoms in Group 1 (e.g., Na, K) lose one electron, while Group 7 elements (e.g., F, Cl) gain one electron during reactions.

Stability is achieved when atoms have a full outer energy level with 8 electrons.
The periodic table is divided into s-block, p-block, d-block, and f-block based on the last orbital filled.
Electron configurations can be determined by reading left to right through each sublevel until reaching the.
element in question.

Patterns and trends on the periodic table help predict how elements will react.
Elements in the same group have the same number of valence electrons, leading to similar reactivity.
Knowledge of valence electron configurations aids in identifying element replacements for reactions.

Trend analysis involves observing size variations when moving down a column or across a row.
The trend is influenced by valence electrons, which are located on the outermost energy level of atoms.
Periodic trends are patterns in element properties across the periodic table:
1. Atomic Radius: Decreases left to right, increases down a group.
2. Ionization Energy: Increases across a period, decreases down a group.
3. Electronegativity: Increases across a period, decreases down a group.
4. Electron Affinity: Becomes more negative across a period, varies down a group.
These trends result from changes in atomic structure, including nuclear charge and electron shielding.

IE is the energy needed to remove an electron from a gaseous atom.
Trends show that IE increases across a period on the periodic table.
Beryllium's significant energy difference for removing the 3rd electron relates to electron location and the octet rule.
The octet rule states that atoms strive to acquire 8 valence electrons for stability.
IE trend explanation involves valence electrons and their energy levels.

Electronegativity measures an element's ability to attract electrons in a chemical bond.
Fluorine, with 7 valence electrons, exhibits high electronegativity due to its strong attraction for additional electrons.
Cesium's low electronegativity is attributed to its single valence electron located far from the nucleus.
Electronegativity values range from 0.70 to 4.00 Paulings, with Fluorine being the most electronegative element.

Linus Pauling, a renowned scientist, made significant contributions to chemistry and biochemistry.
He received Nobel Prizes in Chemistry and Peace, showcasing his diverse expertise.
Pauling's work on the double helix structure of DNA and vitamin C remains influential.
Understanding Pauling's achievements adds depth to the study of electronegativity.