drawBall(x, y, elementName) {
    let ctx = this.ctx;
    ctx.save();
    ctx.beginPath();
    ctx.arc(x + this.offsetX, y + this.offsetY, this.opts.bondLength / 4.5, 0, MathHelper.twoPI, false);
    ctx.fillStyle = this.themeManager.getColor(elementName);
    ctx.fill();
    ctx.restore();
  }
Draw a ball to the canvas.

@param {Number} x The x position of the text.
@param {Number} y The y position of the text.
@param {String} elementName The name of the element (single-letter).