A pure substance consisting entirely of atoms with the same number of protons (same atomic number), which cannot be broken down into simpler substances by chemical means.
A pure substance that can't be broken down chemically. Gold is gold, oxygen is oxygen.
Showing a random 20 of 76 problems.
Example 1
easy
Are all elements solid at room temperature? Give a non-solid example.
Example 2
hard
An element has K-shell, L-shell, M-shell electron counts 2,8,7. Name the element and predict its ion.
Example 3
hard
An element X reacts with oxygen to form X2O3. If 5.40g of X combines with 4.80g of oxygen, what is the molar mass of X? Use M(O)=16.
Example 4
medium
An unknown shiny solid conducts electricity, can be hammered into sheets, and cannot be broken down chemically. What is it likely to be?
Example 5
medium
There are about 118 known elements. Why can these few elements make millions of substances?
Example 6
medium
An element's symbol Cu comes from which language?
Example 7
hard
Element X has Z=79. List its proton count, its likely conductivity, and one common use.
Example 8
medium
A neutral atom contains 15 protons, 16 neutrons, and 15 electrons. Identify the element and its mass number.
Example 9
medium
Sample A has atoms with 8 protons and 8 electrons. Sample B has atoms with 8 protons and 10 electrons. Are they the same element? Explain.
Example 10
easy
Can an element be broken down into simpler substances by chemical means?
Example 11
challenge
Substance 1: only atoms with Z=8. Substance 2: atoms with Z=1 and Z=8. Classify each and name the elements involved.Which is an element and which is a compound?
Example 12
medium
Carbon dioxide (CO2) can be separated into carbon and oxygen. What does this tell you about CO2?
Example 13
medium
An unknown shiny solid conducts electricity and cannot be broken down chemically. What category does it fit?
Example 14
easy
Which of these is a pure element: H2O, Cu, NaCl, CH4?
Example 15
medium
A substance has atoms with proton counts of both 11 and 17. Is it an element or a compound?
Example 16
hard
A 0.500mol sample of an element has a mass of 32.0g. Identify the element and its standard form at room temperature.
Example 17
hard
Determine the number of atoms in 11.5g of pure sodium (Na, M=23.0g/mol). Use NA=6.022×1023mol−1.
Example 18
medium
Sodium (Na) reacts vigorously with chlorine (Cl2) to form NaCl. Was a new element created?
Example 19
easy
How many different elements are present in glucose, C6H12O6?
Example 20
challenge
A 100 g sample is fully decomposed into 60 g of element A and 40 g of element B with nothing left over. Was the original sample an element, and what does mass conservation tell you?Mass conservation: 60 + 40 = 100 g confirms this is a compound.