periodic table, electronegativity atomic radius history

How did Mendeleev arrange the periodic table?

Elements were arranged in order of increasing atomic mass and placed into rows and columns based on recurring patterns in their chemical and physical properties.

What did Mendeleev do to accommodate undiscovered elements?

He left empty spaces in the periodic table for undiscovered elements.

What criteria did Mendeleev use to predict new elements?

He predicted new elements based on atomic mass, density, melting point, and reactivity.

Why are potassium (K) and argon (Ar) out of mass order in the periodic table?

Mendeleev prioritized chemical properties over mass order, placing Ar before K despite K having a greater atomic mass.

What did Mosley discover about the periodic table?

Mosley showed that elements are ordered by atomic number, not atomic mass.

What are the three major classifications of elements in the periodic table?

Metals (left side + middle), Nonmetals (upper right), and Metalloids (stair-step line).

What are the properties of metals?

Metals are conductive, malleable, ductile, and shiny.

What are the properties of nonmetals?

Nonmetals are dull, brittle, and poor conductors.

What are metalloids and where are they located?

Metalloids are semi-conductors with mixed properties, located along the stair-step line in the periodic table.

What are alkali metals and their reactivity?

Alkali metals (Group 1) are very reactive, soft, and form +1 ions.

What are alkaline earth metals and their reactivity?

Alkaline earth metals (Group 2) are reactive but less so than alkali metals and form +2 ions.

What are halogens and their reactivity?

Halogens (Group 17) are very reactive nonmetals that form -1 ions.

What are noble gases and their reactivity?

Noble gases (Group 18) are unreactive due to having full valence shells.

What is the octet rule?

Atoms gain or lose electrons to achieve a full outer shell of eight valence electrons.

Why do cations shrink and anions grow?

Cations shrink because losing electrons removes a shell and protons pull remaining electrons closer; anions grow due to increased repulsion from added electrons.

What is ionization energy (IE)?

IE is the energy required to remove the outermost electron from a gaseous atom.

How does Coulomb's Law relate to atomic size?

Atomic size decreases with stronger attraction (more protons, smaller distance) and increases with weaker attraction (less protons, larger distance).

What factors affect electronegativity (EN)?

Electronegativity increases with more protons, smaller atomic radius, and less shielding.

Why do noble gases have high ionization energy?

They have stable octets, making it energetically unfavorable to remove an electron.

How does reactivity differ between metals and nonmetals?

Metals react by losing electrons (lower ionization energy), while nonmetals react by gaining electrons (higher electronegativity).

How do you determine the number of valence electrons from electron configuration?

Count the electrons in the highest energy level of the configuration.

What is the significance of Lewis Dot Symbols?

They represent the valence electrons of an atom, helping to visualize bonding and reactivity.