Science Test #1

What did Democritus propose?

Matter is made of indivisible particles called “atomos.”

What did Aristotle believe matter was made of?

Earth, air, fire, and water. His theory delayed scientific progress.

What did John Dalton propose, and what was his model?

The Billiard Ball model: atoms are solid spheres. His theory stated that matter is made of atoms, atoms of an element are identical, and atoms combine in constant ratios to form compounds.

What did J.J. Thomson discover and how?

He discovered the electron using cathode rays. The rays were attracted to a positive plate, showing the particles were negatively charged.

What was Thomson’s atomic model?

The Plum Pudding/Raisin Bun model: negative electrons embedded in a positively charged sphere.

What did Rutherford’s Gold Foil experiment show?

Most of the atom is empty space, while a tiny, dense, positively charged nucleus is at the center.

What did each Rutherford observation mean?

Most alpha particles passed through = mostly empty space; some deflected = a nucleus exists; some bounced back = the nucleus is small and positively charged.

What did Niels Bohr propose?

Electrons exist in specific energy levels/shells around the nucleus.

What happens when electrons gain or lose energy?

They gain energy and jump to a higher level; when they lose energy, they return to a lower level and release light.

What did James Chadwick discover?

The neutron, a neutral particle found in the nucleus.

What are the three subatomic particles? Give their charge, location, and approximate mass.

Proton: +, nucleus, 1 amu. Neutron: 0, nucleus, 1 amu. Electron: −, outside nucleus, negligible mass.

What is atomic number?

The number of protons. It identifies the element.

What is mass number?

The number of protons + neutrons.

How do you calculate the number of neutrons?

Mass number − atomic number.

How many electrons does a neutral atom have?

The same number as protons.

What is atomic mass?

The decimal mass value shown on the periodic table. For your class, round it to the nearest whole number to get the mass number

An element has atomic number 17 and mass number 35. Find its protons, neutrons, and electrons.

17 protons, 18 neutrons, 17 electrons.

What is the difference between atomic number and mass number?

Atomic number = protons only. Mass number = protons + neutrons.

Who is known as the “Father” of the periodic table?

Dmitri Mendeleev.

What is a period?

A horizontal row on the periodic table.

What does the period number tell you?

The number of electron shells.

What is a group/family?

A vertical column on the periodic table.

What do groups/families tell you about the main-group elements studied in class?

The number of valence electrons.

What are valence electrons?

Electrons in the outermost electron shell.

An element is in Period 3 and Group IA. What does that tell you?

It has 3 electron shells and 1 valence electron.

What are the Alkali Metals and what are their properties?

Group IA/1. They are very reactive, soft metals; their reactivity increases down the group.

How do Alkali Metals react with water?

They form a base and hydrogen gas.

Is hydrogen an Alkali Metal?

No.

What are the Alkaline Earth Metals and what are their properties?

Group IIA/2. They are metallic solids, harder and less reactive than Alkali Metals.

What are the Halogens and what are their properties?

Group VIIA/17. They are very reactive/toxic non-metals, often colorful, and form salts with metals and strong acids with hydrogen.

What are the Noble Gases and why are they stable?

Group VIIIA/18. They are very stable and non-reactive because they have a full outer electron shell. They are colorless gases.

Where are metals, non-metals, and metalloids located?

Metals = left of the step line; non-metals = right of the step line; metalloids = along/touching the step line.

What are the main properties of metals?

Shiny (lustre), conduct heat and electricity, malleable, and react with acids.

What are the main properties of non-metals?

Dull, brittle if solid, poor conductors, and do not react with acids.

What are metalloids?

Elements with a combination of metallic and non-metallic properties.

What is the purpose of the step line?

It separates metals from non-metals and identifies the general location of metalloids.

What state are most elements at room temperature?

Solid.

Which two elements are liquids at room temperature?

Mercury (Hg) and Bromine (Br).

What state are Noble Gases at room temperature?

Gas.

What does a Bohr-Rutherford model show?

A nucleus containing protons and neutrons, with electrons arranged on full circular shells around it.

What does the simplified atomic model show?

A nucleus with p⁺ and n⁰ counts, plus electron counts on shell arcs.

What is the electron shell capacity rule for the first 20 elements?

2, 8, 8, 2.

How would you represent an atom with 17 electrons using shells?

2, 8, 7.

How do atomic number and atomic mass change across a period and down a family?

Both increase from left to right and from top to bottom.

What happens to atomic radius across a period and down a family? Why?

It decreases across because the nucleus pulls electrons more strongly; it increases down because new electron shells are added.

What happens to ionization energy across a period and down a family? Why?

It increases across because electrons are harder to remove; it decreases down because outer electrons are farther from the nucleus.

What is ionization energy?

The energy required to remove an electron.

What happens to electronegativity across a period and down a family? Why?

It increases across because the nucleus has a stronger pull; it decreases down because the outer electrons are farther away.

What is electronegativity, and what is its value for Noble Gases according to your class material?

Electronegativity is the ability of an atom to attract electrons in a bond. Noble Gases = 0 according to your guide.

What is the general trend for density, melting point, and boiling point?

They generally peak around the middle of the periodic table, particularly among transition metals.