Chemistry Atoms Test

What does the Latin root word for "composition" mean?

Comes from the Latin compositio (from com- "together" + ponere "to put"), meaning "putting together" or "how something is put together/arranged."

What makes a pure substance different from a mixture?

A pure substance has a constant, uniform chemical composition and set properties throughout, while a mixture is a physical combination of two or more substances that retain their individual properties and can vary in proportion.

What is an element?

A pure substance composed of only one type of atom that cannot be broken down into simpler substances by ordinary chemical or physical means.

How many known elements are there?

There are 118 known elements on the periodic table (92 occur naturally, and the rest are synthetic).

What is an atom, and can two different elements have the same type of atom?

The fundamental, smallest unit of an element that retains the chemical identity of that element. No, two different elements cannot have the same type of atom (each element has a unique number of protons).

Name two elements that are liquids at room temperature.

Mercury (Hg) and Bromine (Br).

Name two elements that are solids and two that are gases at room temperature.

Solids: Iron (Fe) and Gold (Au) [or Carbon, Copper]. Gases: Oxygen (O2) and Nitrogen (N2) [or Helium, Hydrogen].

What are the capitalization rules for writing an element's chemical symbol?

The first letter of a chemical symbol is ALWAYS capitalized. If there is a second letter, it is ALWAYS lowercase (e.g., Cu, Zn, Na).

Give the correct chemical symbol for Copper and Zinc.

Copper = Cu | Zinc = Zn

Define a chemical compound.

A pure substance formed when two or more different elements chemically combine in a fixed ratio.

How do the properties of a compound compare to the properties of the elements that form it?

The physical and chemical properties of a compound are completely different from the properties of the individual elements that make it up.

Provide an example showing how water's properties differ from hydrogen and oxygen.

Hydrogen (H2) and Oxygen (O2) are both highly flammable/reactive gases at room temperature, but when combined chemically into water (H2O), they form a stable, non-flammable liquid used to put out fires.

What does it mean for a compound to have a "fixed proportion"?

A compound always contains the exact same elements combined in the exact same numerical or mass ratio, regardless of the size or source of the sample.

Can elements be broken down into simpler substances? Can compounds?

Elements CANNOT be broken down into simpler substances. Compounds CAN be broken down into their constituent elements.

What is required to break a compound apart into its elements?

A chemical reaction/change (chemical means) involving energy input (such as heat or electricity) is required to break a compound apart.

What is electrolysis?

A process that uses an electric current to drive a non-spontaneous chemical reaction, such as breaking water down into hydrogen and oxygen gas.

What does the Law of Definite Proportions state?

States that a given chemical compound always contains its component elements in fixed ratio by mass, regardless of the sample size or source.

Write the formula used to calculate the percent by mass of an element in a compound.

Percent by Mass = (Mass of Element / Total Mass of Compound) * 100

A 10 g sample of a compound contains 2.5 g of oxygen. What is the percent by mass of oxygen in the sample?

25%. Calculation: (2.5 g / 10 g) * 100 = 25%

If you double the size of a water sample from 5 g to 10 g, does the percent by mass of hydrogen change? Explain why

No, doubling the sample size from 5 g to 10 g does NOT change the percent by mass. Because compounds have a fixed proportion (Law of Definite Proportions), both the element mass and compound mass double, keeping the percentage identical.

Where are protons located in an atom, and what is their electrical charge?

Protons are located inside the atomic nucleus and have a positive electrical charge (+1).

What is the atomic number of an element, and why is it important?

The atomic number is the number of protons in the nucleus of an atom. It is important because it identifies the element (every element has a unique atomic number).

Which subatomic particle has no electrical charge, and where