unit 1 chem

What are the three subatomic particles, their charges, and where are they located in the atom?

Proton: Positive (+1), inside the nucleus. / Neutron: Neutral (0), inside the nucleus. / Electron: Negative (-1), orbits outside the nucleus in electron clouds.

What is the difference between Atomic Number (Z) and Mass Number (A)?

Atomic Number (Z) is the number of protons and defines the element's identity. Mass Number (A) is the total number of protons and neutrons combined.

What is an isotope? Give a quick analogy.

An atom with the same number of protons (same element) but a different number of neutrons, changing its weight. Analogy: An iPhone 15 with 128GB vs. 256GB—same phone, slightly different weight/storage.

What is an ion, and what are the two specific types?

An ion is a charged atom that has gained or lost electrons. Cation: A positively charged ion (lost electrons). Anion: A negatively charged ion (gained electrons).

What are the memory tricks to remember Cations vs. Anions?

Ca+ion: The letter "t" looks like a plus sign (+) -> Positive. Or remember: "Cats have paws" (positive). Anion: Looks like "A Negative Ion".

How do you calculate the number of Neutrons and Electrons in an ion?

Neutrons = Mass Number - Atomic Number.

Electrons (Cation / + charge) = Protons - Charge.

Electrons (Anion / - charge) = Protons + Charge.

What is the difference between a Period and a Group on the periodic table?

Period (Horizontal Row): Elements have the same number of electron shells (layers). Group/Family (Vertical Column): Elements have the same number of valence electrons and similar chemical behaviors.

What are valence electrons and why do they matter?

They are the electrons located in the absolute outermost shell of an atom. They matter because they are the only electrons involved in forming chemical bonds and chemical reactions.

What is Atomic Radius and what is its trend?

The physical size of an atom. It INCREASES going down a group (adds a new layer of electrons) and DECREASES going left-to-right across a period (more protons pull the same shell closer).

What is Ionization Energy and what is its trend?

The energy needed to rip an electron away from an atom. It DECREASES going down a group (electrons are farther from the nucleus, easier to steal)

and INCREASES going left-to-right across a period (atoms are smaller and cling tightly to electrons).

What are Electronegativity and Electron Affinity? What is their trend?

The measurement of how strongly an atom grabs or pulls nearby electrons.

Both DECREASE going down a group (nucleus is buried deep, weaker pull) and

INCREASE going left-to-right across a period (atoms are tiny and desperate to fill their outer shell).

Noble gases are exceptions (0 value).

What are the two elemental "Mental Anchors" for periodic trends?

Francium (Fr - bottom left): The absolute biggest atom; has the lowest ionization energy and electronegativity (holds electrons loosely). Fluorine (F - top right): A tiny, fierce atom; has the highest ionization energy and highest electronegativity (hoards its own and steals others).

What is the fundamental difference between an ionic bond and a covalent bond?

Ionic bonds involve the complete transfer of electrons from a metal to a non-metal. Covalent bonds involve the sharing of electron pairs between non-metals.

What is the rule for placing dots in a Lewis structure for a single atom?

Find the valence electron count from the group number. Place single dots on the four sides (top, right, bottom, left) one by one before pairing them up.

How do you represent ionic vs covalent bonds in Lewis diagrams?

Ionic: Use brackets around the symbols with the net charge outside the brackets (no lines). Covalent: Use solid lines between chemical symbols to represent shared electron pairs.

What is the difference between a lone pair and a bonding pair?

A lone pair consists of two valence electrons localized on a single atom (drawn as dots). A bonding pair is a pair of electrons shared between two atoms (drawn as a line).

What makes a covalent bond polar vs non-polar?

A bond is polar if electrons are shared unequally due to a difference in electronegativity, creating partial charges. It is non-polar if electrons are shared equally.

How can a molecule contain polar bonds but be non-polar overall?

If the molecule is perfectly symmetrical, the individual polar pulls (dipoles) point in opposite directions and completely cancel each other out.

What does the acronym SNAP stand for in molecular polarity?

Symmetrical is Non-polar, Asymmetrical is Polar.

Does the concept of molecular polarity apply to ionic compounds?

No. Polarity only applies to covalent sharing. Ionic compounds completely transfer electrons, forming full, permanent mathematical charges in a repeating grid (crystal lattice) rather than individual molecules.

What is the core rule of VSEPR theory?

Valence Shell Electron Pair Repulsion states that

electron pairs around a central atom repel each other and will push apart as far as possible to minimize repulsion, determining the 3D shape of the molecule.

Why do lone pairs alter bond angles more than shared bonding pairs?

Lone pairs are electron hogs; they are unbonded and take up more physical space around the central atom, pushing shared bonding lines closer together.

What VSEPR shape and bond angle do you get with 4 bonding pairs and 0 lone pairs?

Tetrahedral shape with a bond angle of 109.5 degrees (e.g., CH4).

What VSEPR shape and bond angle do you get with 3 bonding pairs and 1 lone pair?

Trigonal Pyramidal shape with a bond angle of 107.3 degrees (e.g., NH3).

What VSEPR shape and bond angle do you get with 2 bonding pairs and 2 lone pairs?

Bent shape with a bond angle of 104.5 degrees (e.g., H2O).