Chemistry: Matter and Atomic Structure

What is a pure substance?

Matter that cannot be separated by a physical process and has a fixed composition.

What is the difference between an element and a compound?

An element is the simplest form of matter that retains its properties (cannot be broken down further), while a compound consists of two or more different elements chemically combined.

What is a homogeneous mixture vs. a heterogeneous mixture?

A homogeneous mixture looks the same throughout (solutions like saltwater), whereas a heterogeneous mixture is not uniform throughout (you can see different parts, like ice water or a cookie).

How would you classify Mercury (Hg) on the matter flowchart?

Pure substance -> Element.

How would you classify iced water?

Mixture -> Heterogeneous mixture.

What are the 4 main indicators that a chemical reaction has occurred?

Gas formed (bubbles/odor), color change, temperature change, and precipitate formed (solid forms from liquids).

In standard periodic table block notation, what do red, blue, black, and white element symbols typically indicate regarding states of matter?

Red = Gas, Blue = Liquid, Black = Solid, White = Synthetic / man-made / artificially created.

What does the atomic number of an element represent?

The number of protons in the nucleus of that atom (which defines the element).

What are the three main subatomic particles, their locations, and their charges?

Proton: in nucleus (+1). Neutron: in nucleus (0). Electron: outside nucleus (-1).

Which subatomic particle determines the identity of an element?

Protons. Changing the number of protons changes what element it is.

What creates an isotope?

Changing the number of neutrons in an atom of the same element (creates a different mass).

What creates an ion?

Changing the number of electrons in an atom (creates an electrical charge).

How do you calculate the number of neutrons in an atom?

Mass Number - Atomic Number = Neutrons.

Who proposed the Plum Pudding Model and what was discovered?

J.J. Thompson. He discovered negatively charged particles called corpuscles or electrons embedded in a positive 'soup'.

What was Ernest Rutherford's major contribution through the Gold Foil Experiment?

He discovered the nucleus—finding that atoms are mostly empty space with a dense, positively charged center containing protons.

What is the key feature of Neils Bohr's Planetary Model?

Electrons orbit the nucleus in specific energy levels or shells.

What does Werner Heisenberg's Quantum (Cloud) Model state about electrons?

It is impossible to know both the exact momentum and position of an electron at the same time; instead, electrons exist in orbitals (regions of probability) shown as a cloud.

In isotopic notation, what do letters A, Z, X, and C stand for?

A = Mass number (Protons + Neutrons), Z = Atomic number (Protons), X = Chemical symbol, C = Charge.

If an atom has 9 protons, 9 neutrons, and 9 electrons, what element is it and what is its charge?

Fluorine (atomic number 9), with a neutral charge (charge = 0).

How do you find the number of electrons in an ion with a charge?

Take the number of protons and subtract the charge (e.g., protons = 13 and charge = +3, electrons = 13 - 3 = 10).

What happens to the charge of a neutral atom if you add two electrons?

It becomes a negative ion (anion) with a -2 charge.

What happens to the change of a neutral atom if you take awwy 2 electrons?

It becomes a positive ion (cation) with a +2 change

What are the reletive masses of Proton Neutron and eletrons?

proton 1amu

neutron 1amu

eletron 0amu