10.4 Chemistry and Electricity Essentials

10.4 Chemistry and Electricity Essentials

A handful of Physical Science items each form test basic chemistry and electricity. These are fast points if you have the building blocks memorized.

Atomic structure

Every atom has a dense central nucleus containing protons (positive charge) and neutrons (no charge), surrounded by electrons (negative charge) in shells.

The atomic number equals the number of protons and uniquely defines the element — every carbon atom has 6 protons. The mass number = protons + neutrons. Isotopes are atoms of the same element with different neutron counts (carbon-12 vs carbon-14). A neutral atom has equal protons and electrons; gaining or losing electrons creates an ion.

The periodic table

Elements are arranged by increasing atomic number. Groups (vertical columns) share similar chemical behavior — Group 1 are reactive alkali metals, Group 18 are inert noble gases. Periods (horizontal rows) share the same number of electron shells. Useful anchors: H is element 1, O is 8, the most abundant gas in Earth's atmosphere is nitrogen (~78%), followed by oxygen (~21%).

States of matter and pH

The four common states, in order of increasing energy, are solid → liquid → gas → plasma. Phase changes: melting (solid→liquid), freezing (liquid→solid), evaporation/boiling (liquid→gas), condensation (gas→liquid), and sublimation (solid→gas directly, like dry ice). The pH scale runs 0-14: below 7 is acidic, exactly 7 is neutral (pure water), above 7 is basic/alkaline.

Electricity

Ohm's law is the must-know relationship: V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). Rearranged: I = V/R and R = V/I. Electrical power is P = IV (watts), or equivalently P = I²R.

• Series circuit: components in a single loop; current is the same everywhere and resistances add (R_total = R1 + R2 + ...). One break stops the whole circuit — like old-style string lights.
• Parallel circuit: multiple branches; voltage is the same across each branch and total resistance is lower than the smallest single resistor. One branch failing leaves the others working — household wiring is parallel.

Worked example

A 12-V battery drives a circuit with 4 ohms of resistance. What is the current? Using I = V/R = 12 / 4 = 3 amperes. Power delivered = P = IV = 3 × 12 = 36 watts.

Common traps

• Confusing atomic number (protons, defines the element) with mass number (protons + neutrons).
• Thinking pH 7 is acidic — 7 is neutral; lower numbers are more acidic.
• Reversing Ohm's law — remember V = IR, so current rises when resistance falls.
• Assuming series circuits lower resistance — series adds resistance; parallel lowers it.
• Believing electrons sit in the nucleus — only protons and neutrons do; electrons orbit outside it.

Chemical bonds and reactions

Atoms combine to fill their outer electron shells. Ionic bonds form when one atom transfers electrons to another, creating charged ions that attract (sodium chloride, table salt). Covalent bonds form when atoms share electrons (water, H₂O). A molecule is two or more atoms bonded together; a compound is a molecule of two or more different elements. In a chemical reaction, atoms rearrange but are never created or destroyed — the law of conservation of mass means a balanced equation has equal atoms of each element on both sides.

Recognize the difference between a physical change (ice melting — same substance, new state) and a chemical change (iron rusting, wood burning — new substances formed).

Acids, bases, and common substances

Acids release hydrogen ions and taste sour (lemon juice, vinegar, stomach acid sit low on the pH scale around 2-3); bases release hydroxide ions and feel slippery (soap, ammonia, bleach sit high, around 11-13). When an acid and base combine they neutralize, producing water and a salt. Pure water is neutral at pH 7. The scale is logarithmic, so each whole step is a tenfold change in acidity — pH 4 is ten times more acidic than pH 5. These facts power quick recall items that simply ask whether a named substance is an acid or a base.

Electrical safety and circuits in practice

Current flows only in a closed circuit; an open switch breaks the loop and stops it. Conductors (copper, aluminum, most metals) let electrons move freely; insulators (rubber, glass, plastic) resist flow and are used for safety coatings. A fuse or circuit breaker protects wiring by interrupting current that climbs too high. Direct current (DC, from batteries) flows one way; alternating current (AC, from wall outlets and the grid) reverses direction many times per second.

Tying this back to Ohm's law: for a fixed voltage, lowering resistance raises current, which is exactly why a short circuit — near-zero resistance — produces a dangerous current surge.

Magnetism and electromagnetism

Magnets have a north and south pole; like poles repel and opposite poles attract, and you cannot isolate a single pole. Moving electric charges create magnetic fields, and moving magnets induce electric currents — this two-way link is electromagnetism, the principle behind motors (electricity into motion) and generators (motion into electricity). Coiling a current-carrying wire makes an electromagnet whose strength rises with more turns and more current.

The same induction principle powers transformers that step voltage up or down across the power grid, making it one of the highest-leverage ideas to understand for both the electricity and the everyday-technology items on the subtest.